Implement enhanced structure and content alignment validation (sub-tasks 6.2-6.4)

## Enhanced Structure Validator (6.3)
- Comprehensive pedagogical pattern validation with educational flow analysis
- Content-type specific structure requirements and section validation
- Advanced section detection with quality scoring and pedagogical purpose identification
- Configurable validation thresholds and auto-fix capabilities for missing sections
- Learning objectives validation with Bloom's taxonomy alignment

## Content Alignment Validator (6.4)
- Cross-content consistency validation between slides, worksheets, quizzes, and guides
- Learning objective alignment analysis with coverage scoring
- Topic extraction and consistency checking across related materials
- Terminology standardization with variant detection (plurals, verb forms)
- Difficulty progression validation and assessment alignment
- Session-based content repository for multi-content validation

## Readability Validator Enhancements (6.2)
- Configurable age-specific and complexity-level thresholds
- Multiple readability metrics (Flesch Reading Ease, Flesch-Kincaid Grade Level)
- Educational content optimization with content-type specific configurations
- Enhanced syllable counting and sentence pattern analysis

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

Co-Authored-By: Claude <noreply@anthropic.com>

Author: michael-borck

src-tauri/src/export/markdown.rs

@@ -68,13 +68,15 @@ impl MarkdownConverter {
 
         // Split content into slides (assuming slides are separated by slide markers)
         let slides: Vec<&str> = content.split("---SLIDE---").collect();
+        let mut slide_count = 0;
 
-        for (i, slide) in slides.iter().enumerate() {
+        for slide in slides.iter() {
             if slide.trim().is_empty() {
                 continue;
             }
 
-            formatted.push_str(&format!("### Slide {}\n\n", i + 1));
+            slide_count += 1;
+            formatted.push_str(&format!("### Slide {}\n\n", slide_count));
             formatted.push_str(&slide.trim());
             formatted.push_str("\n\n");
 
@@ -334,8 +336,7 @@ impl FormatConverter for MarkdownConverter {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::content::{ContentType, ContentMetadata};
-    use std::path::PathBuf;
+    use crate::content::{ContentType, generator::ContentMetadata};
 
     fn create_test_content() -> GeneratedContent {
         GeneratedContent {