Add Godot language and scene graph support

[KirisamaMarisa]

Summary

Adds first-class Godot project indexing for CodeGraph, covering GDScript scripts plus Godot scene/resource files.

• index GDScript classes, methods, variables, constants, signals, exports, annotations, preload/load references, and node lookups
• extract .tscn/.tres scenes/resources as graph nodes, including scene components, ExtResource/SubResource ids, attached scripts, instanced scenes, signal connections, and resource paths
• resolve Godot-specific references across scripts and scenes, including res:// paths, $/% node paths, find_child/get_node-style lookups, helper wrapper lookups, dynamic node-name constants, and scene instance callers
• expose Godot resource paths and scene node names through CLI/MCP callers, callees, impact, query, and status flows
• report resolved edge counts after indexing so index output matches status more closely
• update agent instructions so Godot resource paths and scene node names are treated as queryable symbols

Validation

• npm.cmd run build
• npx vitest run tests/extraction.test.ts -t "Godot Resource Extraction"
• npx vitest run tests/installer-targets.test.ts
• rebuilt the CodeGraph index for a local Godot 4 validation project
• real CodeGraph MCP checks against the local validation project: status, search, callers, callees, impact

Real project smoke result: the local Godot validation project indexed 1,203 files with 41,113 nodes and 78,824 edges; queries successfully linked scene nodes, @onready $ node paths, res:// scene references, scene instances, and signal handler relationships.

[miracle-kang]

+1 for this PR. Godot support would be really valuable for my workflow as well.
Thanks for putting this together, I hope the maintainers can review and consider merging it.