feat(mcp): add dev_history adapter for git history search (#93)

[prosdev]

Summary

Adds the dev_history MCP tool for semantic search over git commit history and file-specific history retrieval.

Changes

HistoryAdapter (packages/mcp-server/src/adapters/built-in/history-adapter.ts)

Tool: dev_history

Two modes of operation:

1. Semantic Search (query): Search commit messages by meaning

   • "authentication token expiry fix" → finds relevant commits
   • Uses GitIndexer for vector similarity search

2. File History (file): Get history for a specific file

   • Uses GitExtractor directly with --follow for rename tracking
   • Supports since and author filters

Parameters:

• query: Semantic search over commit messages
• file: Get history for a specific file path
• limit: Maximum commits to return (1-50, default: 10)
• since: Date filter (ISO or relative like "2 weeks ago")
• author: Filter by author email
• tokenBudget: Maximum tokens for output (100-10000, default: 2000)

Output includes:

• Commit hash, subject, author, date
• File change stats (+additions, -deletions)
• Issue/PR references
• Files changed (abbreviated)
• Body for first commit

MCP Server Integration

• Added HistoryAdapter to built-in adapters
• Created separate VectorStorage for git commits (-git suffix)
• Proper shutdown handling for git vector storage

Tests

• 17 comprehensive unit tests covering:
  • Semantic search functionality
  • File history retrieval
  • Input validation
  • Output formatting
  • Token budgeting
  • Error handling

Example Usage

# Semantic search
dev_history query="authentication token expiry"

# File history
dev_history file="src/auth/token.ts" since="2 weeks ago"

Closes

Closes #93

Part of

Epic: Intelligent Git History (v0.4.0) #90