Nested .gitignore patterns not respected during indexing

[dergachoff]

.output is listed in webapp/. gitignore, but webapp/. output/** files were fully indexed (thousands of minified bundle nodes). The layered ignore system appears to only read the root .gitignore, not nested ones in subdirectories.

Repo structure:

  .gitignore          # has dist/
  webapp/.gitignore   # has .output
  webapp/.output/     # ← fully indexed despite ignore

This caused build artifacts to dominate query results — every high-degree function, every search hit was from minified bundles.

[dLo999]

PR created: #183

Root cause: walk_dir in discover.c only used the root .gitignore — subdirectory .gitignore files were never loaded.

Fix: walk_dir now checks for .gitignore in each subdirectory, loads it, and matches paths relative to that directory. Patterns propagate to recursive calls.

Verified with the exact scenario from the issue: webapp/.gitignore with .output now correctly excludes webapp/.output/ files.

Changes: src/discover/discover.c, tests/test_discover.c (+3 tests)