[Feature] AST-Based Call Graph Traversal & Relationship Tracing (trace_path MCP Tool)

[spelech]

This change extends ContextCortex with AST-based call graph relationship extraction and the trace_path MCP tool for BFS call graph traversal.

Key additions:

• Extended SQLite relational schema in app/services/db.py with indexed ast_relationships table and ON DELETE CASCADE foreign key constraints.
• Updated Tree-sitter parsing in app/services/chunker.py and models in app/models/schemas.py to extract CALLS, IMPORTS, INHERITS, and IMPLEMENTS relationships across supported programming languages.
• Updated ingestion and deletion pipelines in app/services/indexer.py to store and purge ast_relationships records linked to symbol IDs.
• Implemented trace_symbol_path BFS graph traversal engine in app/services/search.py with cycle/recursion protection, direction filtering, depth clamping, limit truncation, and Markdown tree output with permalinks.
• Registered trace_path MCP tool in app/mcp/tools.py and app/mcp/mcp_server.py.
• Added comprehensive unit and integration tests in tests/backend/test_ast_relationships.py and tests/backend/test_trace_path.py.

Fixes #1

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PR created automatically by Jules for task 14592028422703187058 started by @spelech

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[spelech]

Code Review: AST Call Graph Traversal & Relationship Tracing (PR #7)

✅ Verification & Findings:

• AST Relationship Extraction: Extracts CALLS, IMPORTS, INHERITS, and IMPLEMENTS edges across Python, JS/TS, Go, Rust, C#, and Java into indexed SQLite ast_relationships table.
• Cycle-Protected BFS Traversal: trace_symbol_path handles recursive and mutually recursive calls cleanly, with direction filtering (callers, callees, both), depth clamping (1-5), limit truncation, and markdown tree rendering.
• FastMCP Tool: Registered trace_path on FastMCP server.
• Test Suite Verification: All 264 unit, integration, and regression tests passing.

Ready for merge once CI checks finish.