feat: Add Student Learning Space DTOs (v2.1.0)

Complete DTO layer for Student Learning Space features, enabling API endpoints
for AI-powered learning assistance, video annotations, and transcript search.

DTOs Added (5 files):

1. AIChat DTOs (2 files):
   - AIChatMessageDto: Request DTO with lesson context and video timestamp
   - AIChatResponseDto: Response with context metadata and token usage
   - AIContextInfoDto: Context tracking (transcript used, notes used)

2. AITakeaways DTOs (1 file):
   - VideoKeyTakeawaysDto: AI-generated key points from video lessons
   - TakeawayDto: Individual takeaway with category and relevance score
   - TakeawayMetadataDto: Processing metadata

3. VideoBookmarks DTOs (1 file):
   - VideoBookmarkDto: Bookmark response with timestamp and label
   - CreateVideoBookmarkDto: Bookmark creation with validation
   - UpdateVideoBookmarkDto: Bookmark label update

4. VideoTranscript DTOs (1 file):
   - TranscriptSearchResultDto: Search results with match count
   - TranscriptSearchMatchDto: Individual match with relevance score

Features Enabled:
- AI chatbot with lesson-aware responses
- Video timestamp-based annotations
- AI-generated key takeaways with categories
- Video bookmarks (manual and AI-generated)
- Full-text transcript search with highlighting

Validation:
- All input DTOs have comprehensive DataAnnotations
- String length limits prevent DoS attacks
- Range validation on numeric fields
- Regex validation on enum-like string fields

Related:
- Entities: StudentNote, VideoBookmark, VideoTranscriptMetadata,
           AIKeyTakeawaysMetadata, AIConversation
- Migration: 20251119000000_AddStudentLearningSpaceEntities
- Database: 54 tables operational

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: marypas74

src/InsightLearn.Core/DTOs/AIChat/AIChatMessageDto.cs

@@ -0,0 +1,33 @@
+using System;
+using System.ComponentModel.DataAnnotations;
+
+namespace InsightLearn.Core.DTOs.AIChat
+{
+    /// <summary>
+    /// DTO for sending a message to AI chatbot.
+    /// Part of Student Learning Space v2.1.0.
+    /// </summary>
+    public class AIChatMessageDto
+    {
+        [Required(ErrorMessage = "Message content is required")]
+        [StringLength(2000, MinimumLength = 1, ErrorMessage = "Message must be between 1 and 2000 characters")]
+        public string Message { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Session ID for conversation continuity.
+        /// If null, a new session will be created.
+        /// </summary>
+        public Guid? SessionId { get; set; }
+
+        /// <summary>
+        /// Optional lesson context for AI responses.
+        /// </summary>
+        public Guid? LessonId { get; set; }
+
+        /// <summary>
+        /// Current video timestamp (in seconds) for contextual responses.
+        /// </summary>
+        [Range(0, int.MaxValue, ErrorMessage = "Video timestamp must be non-negative")]
+        public int? VideoTimestamp { get; set; }
+    }
+}

src/InsightLearn.Core/DTOs/AIChat/AIChatResponseDto.cs

@@ -0,0 +1,36 @@
+using System;
+
+namespace InsightLearn.Core.DTOs.AIChat
+{
+    /// <summary>
+    /// AI chatbot response DTO.
+    /// Part of Student Learning Space v2.1.0.
+    /// </summary>
+    public class AIChatResponseDto
+    {
+        public Guid SessionId { get; set; }
+        public string Response { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Timestamp when response was generated.
+        /// </summary>
+        public DateTime Timestamp { get; set; }
+
+        /// <summary>
+        /// Context used for generating the response.
+        /// </summary>
+        public AIContextInfoDto? Context { get; set; }
+    }
+
+    /// <summary>
+    /// Context information used by AI for response generation.
+    /// </summary>
+    public class AIContextInfoDto
+    {
+        public Guid? LessonId { get; set; }
+        public int? VideoTimestamp { get; set; }
+        public bool TranscriptUsed { get; set; }
+        public bool NotesUsed { get; set; }
+        public int TokensUsed { get; set; }
+    }
+}

src/InsightLearn.Core/DTOs/AITakeaways/VideoKeyTakeawaysDto.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+
+namespace InsightLearn.Core.DTOs.AITakeaways
+{
+    /// <summary>
+    /// AI-generated key takeaways for a video lesson.
+    /// Part of Student Learning Space v2.1.0.
+    /// </summary>
+    public class VideoKeyTakeawaysDto
+    {
+        public Guid LessonId { get; set; }
+
+        /// <summary>
+        /// List of AI-extracted key takeaways.
+        /// </summary>
+        public List<TakeawayDto> Takeaways { get; set; } = new();
+
+        /// <summary>
+        /// Processing metadata.
+        /// </summary>
+        public TakeawayMetadataDto? Metadata { get; set; }
+    }
+
+    /// <summary>
+    /// Single key takeaway with category and relevance.
+    /// </summary>
+    public class TakeawayDto
+    {
+        public string TakeawayId { get; set; } = string.Empty;
+        public string Text { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Category: CoreConcept, BestPractice, Example, Warning, Summary.
+        /// </summary>
+        public string Category { get; set; } = "CoreConcept";
+
+        /// <summary>
+        /// AI relevance score (0.0 - 1.0).
+        /// </summary>
+        public double RelevanceScore { get; set; }
+
+        public double? TimestampStart { get; set; }
+        public double? TimestampEnd { get; set; }
+
+        /// <summary>
+        /// User feedback (thumbs up/down).
+        /// </summary>
+        public int? UserFeedback { get; set; }
+    }
+
+    /// <summary>
+    /// Takeaway processing metadata.
+    /// </summary>
+    public class TakeawayMetadataDto
+    {
+        public int TotalTakeaways { get; set; }
+        public string ProcessingModel { get; set; } = string.Empty;
+        public DateTime ProcessedAt { get; set; }
+    }
+}

src/InsightLearn.Core/DTOs/VideoBookmarks/VideoBookmarkDto.cs

@@ -0,0 +1,65 @@
+using System;
+using System.ComponentModel.DataAnnotations;
+
+namespace InsightLearn.Core.DTOs.VideoBookmarks
+{
+    /// <summary>
+    /// Video bookmark response DTO.
+    /// Part of Student Learning Space v2.1.0.
+    /// </summary>
+    public class VideoBookmarkDto
+    {
+        public Guid Id { get; set; }
+        public Guid UserId { get; set; }
+        public Guid LessonId { get; set; }
+
+        /// <summary>
+        /// Video timestamp in seconds.
+        /// </summary>
+        public int VideoTimestamp { get; set; }
+
+        /// <summary>
+        /// Optional custom label.
+        /// </summary>
+        public string? Label { get; set; }
+
+        /// <summary>
+        /// Manual (user-created) or Auto (AI-generated from key takeaways).
+        /// </summary>
+        public string BookmarkType { get; set; } = "Manual";
+
+        public DateTime CreatedAt { get; set; }
+    }
+
+    /// <summary>
+    /// DTO for creating a video bookmark.
+    /// </summary>
+    public class CreateVideoBookmarkDto
+    {
+        [Required(ErrorMessage = "Lesson ID is required")]
+        public Guid LessonId { get; set; }
+
+        [Required(ErrorMessage = "Video timestamp is required")]
+        [Range(0, int.MaxValue, ErrorMessage = "Video timestamp must be non-negative")]
+        public int VideoTimestamp { get; set; }
+
+        [StringLength(200, ErrorMessage = "Label must be 200 characters or less")]
+        public string? Label { get; set; }
+
+        /// <summary>
+        /// Bookmark type: Manual or Auto.
+        /// Default: Manual.
+        /// </summary>
+        [RegularExpression("^(Manual|Auto)$", ErrorMessage = "Bookmark type must be Manual or Auto")]
+        public string BookmarkType { get; set; } = "Manual";
+    }
+
+    /// <summary>
+    /// DTO for updating a video bookmark.
+    /// </summary>
+    public class UpdateVideoBookmarkDto
+    {
+        [StringLength(200, ErrorMessage = "Label must be 200 characters or less")]
+        public string? Label { get; set; }
+    }
+}

src/InsightLearn.Core/DTOs/VideoTranscript/TranscriptSearchResultDto.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Collections.Generic;
+
+namespace InsightLearn.Core.DTOs.VideoTranscript
+{
+    /// <summary>
+    /// Transcript search result DTO.
+    /// Part of Student Learning Space v2.1.0.
+    /// </summary>
+    public class TranscriptSearchResultDto
+    {
+        public Guid LessonId { get; set; }
+        public string Query { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Total number of matches found.
+        /// </summary>
+        public int TotalMatches { get; set; }
+
+        /// <summary>
+        /// List of matching segments with context.
+        /// </summary>
+        public List<TranscriptSearchMatchDto> Matches { get; set; } = new();
+    }
+
+    /// <summary>
+    /// Single search match with highlighted text.
+    /// </summary>
+    public class TranscriptSearchMatchDto
+    {
+        public double Timestamp { get; set; }
+        public string Text { get; set; } = string.Empty;
+        public string? Speaker { get; set; }
+
+        /// <summary>
+        /// Relevance score (0.0 - 1.0).
+        /// </summary>
+        public double RelevanceScore { get; set; }
+    }
+}