fix: add Julia (.jl) support for code indexing with fallback chunking

[roomote]

This PR attempts to address Issue #8966. Feedback and guidance are welcome.

Problem

Julia files (.jl) were not being indexed at all because:

1. The .jl extension was not in the supported extensions list
2. Without being in the extensions list, files were rejected before fallback chunking could be applied
3. This meant Julia code was completely invisible to the codebase search feature

Solution

• Added .jl to the supported extensions list in tree-sitter/index.ts
• Added .jl to the fallbackExtensions array in shared/supported-extensions.ts
• This enables Julia files to use fallback chunking for code indexing when tree-sitter parsing is not available

Testing

• Added comprehensive test suite in parser.julia.spec.ts that verifies:
  • Julia files use fallback chunking
  • Small files below minimum size are handled correctly
  • Large files are chunked appropriately
  • Extension detection is case-insensitive
• All existing tests continue to pass

Impact

• Non-tree-sitter supported languages (like Julia) will now be properly indexed using fallback chunking
• Users can now search their Julia codebase effectively
• The same approach can be used to add support for other languages without tree-sitter parsers

Fixes #8966

---

Important

Add support for Julia files by enabling fallback chunking and updating supported extensions.

• Behavior:
  • Add .jl to supported extensions in tree-sitter/index.ts and fallbackExtensions in shared/supported-extensions.ts.
  • Enables fallback chunking for Julia files when tree-sitter parsing is unavailable.
• Testing:
  • New test suite parser.julia.spec.ts verifies fallback chunking for Julia files.
  • Tests include handling of small files, large files, and case-insensitive extension detection.
• Impact:
  • Julia files are now indexed using fallback chunking, improving searchability.
  • Approach can be extended to other non-tree-sitter languages.

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[roomote]

✅ Review complete - no issues found. The implementation correctly adds Julia (.jl) support with fallback chunking and includes comprehensive test coverage.

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[daniel-lxs]

#8966 (comment)