Make .blarignore additive to .gitignore for automatic exclusion

[rysweet]

Summary

This PR implements automatic .gitignore support in Blarify, making .blarignore additive to .gitignore patterns. This ensures that files ignored by git (like node_modules, .env, build artifacts) are automatically excluded from the graph analysis.

Changes

• ✅ Added pathspec dependency for proper gitignore pattern parsing
• ✅ Created GitignoreManager class to handle .gitignore file parsing and caching
• ✅ Modified ProjectFilesIterator to support gitignore integration
• ✅ Updated GraphBuilder API to expose gitignore configuration options
• ✅ Added comprehensive test suite covering various gitignore scenarios
• ✅ Updated documentation with gitignore feature details

Benefits

• 🚀 Automatic exclusion of git-ignored files
• 🔄 Reduced maintenance burden (no need to duplicate patterns)
• ⚡ Better performance by skipping unnecessary files
• 🎯 Consistent behavior with git

How it works

1. Automatic loading: All .gitignore files in the project are automatically found and parsed
2. Additive behavior: .blarignore adds additional exclusions on top of .gitignore
3. Full pattern support: Supports all gitignore syntax including globs, negations*, and comments
4. Configurable: Can be disabled if needed via use_gitignore=False

*Note: Complex negation patterns (e.g., \!build/keep/) are not fully supported yet and will be addressed in a follow-up PR.

Testing

• ✅ Files in .gitignore are excluded
• ✅ .blarignore patterns work additively
• ✅ Nested .gitignore files are respected
• ✅ Feature can be disabled
• ⏭️ Negation patterns (marked as skip, to be addressed later)

Example Usage

# Gitignore support is enabled by default
graph_builder = GraphBuilder(root_path="/path/to/project")

# Or explicitly configure
graph_builder = GraphBuilder(
    root_path="/path/to/project",
    use_gitignore=True,  # Default
    blarignore_path="/custom/path/.blarignore"  # Optional
)

Fixes #6