feat: add relationship tracking for GDScript

[nguyenchiencong]

Summary

Adds full relationship tracking for GDScript, including call, signal emission, extends, and preload dependency extraction, and wires those relationships into parser and MCP integration tests.

Changes

• Taught GdscriptParser to collect call targets (including emit_signal) and type/resource uses from extends, preload constants, and script-level loads.
• Added GDScript fixture scripts that exercise signals, preload constants, and reset behavior for tests.
• Introduced parser test coverage to ensure find_calls and find_uses report the expected edges.
• Added an integration test that indexes the fixtures, runs MCP semantic search, and verifies analyze_impact succeeds using the new relationships.

Technical Details

• Added helpers to strip quotes and extract signal/preload targets, plus recursive walkers that propagate scope context and avoid duplicate preload edges.
• All constants are registered with a shared <script> scope to align extends/use output with other languages.
• Integration test enables semantic search, indexes fixtures, and pulls symbol IDs from MCP semantic_search_with_context output before calling analyze_impact.

Test Coverage

• cargo test tests::parsers_gdscript::test_relationships
• cargo test --test integration_tests test_gdscript_mcp

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