feat(extraction): add GDScript language support

[Plumvery]

Summary

Adds GDScript (.gd, Godot Engine) as a supported language on the wasm extraction path, following the shape of previous language additions (Nix #1190, ArkTS #648).

• Extractor (src/extraction/languages/gdscript.ts, ~100 lines): functions with typed signatures, _init constructors, inner classes with methods, the full var/const/@export/@onready variable family, signals, enums with members, static func detection, and call edges through call / attribute_call / base_call.
• Grammar: PrestonKnopp/tree-sitter-gdscript v6.1.0 (MIT), vendored as an ABI-15 wasm rebuilt from upstream source (tree-sitter-cli 0.25.10 generate + build --wasm, emscripten/emsdk:4.0.4), external scanner (indentation) included — the same approach as the Nix wasm.

Grammar shapes that needed care

• The var/const family names its target via a name-typed child, not identifier, so the core's generic variable fallback can't read them. A visitNode hook creates variable/constant nodes itself, then walks initializers so calls inside them (preload(...), Foo.new()) are captured.
• func _init(...) (constructor_definition) has no name field — resolveName supplies the conventional _init. enumerator names its identifier via left.
• static on functions is a named static_keyword child with no field (the var statements carry it via a field) — a child scan covers both.
• signal foo(a, b) extracts as a property carrying the parameter list, so connect()-heavy scripts expose their signal surface in the graph.
• obj.method(args) parses as attribute(identifier, attribute_call(...)) — attribute_call joins callTypes and the core's namedChild(0) callee fallback yields the bare method name (name-match resolution, same as self/this receivers elsewhere).

Validation

scripts/add-lang/check-grammar.mjs: ABI 15, 20/20 clean parses, heap-safe under multi-grammar reuse (the Lua ABI-13 corruption scenario this script exists for does not occur).

scripts/add-lang/verify-extraction.mjs criteria on two corpora (all critical and soft checks pass):

Corpus	.gd files	nodes	edges	index time
godotengine/godot-demo-projects (public)	461	5,216	6,783	3.7s
Private Godot 4 game	138	2,996	11,484	1.8s

Kind spread on the public corpus: 2,027 functions / 184 methods / 45 classes / 141 signals→properties / 39 enums + 130 members / 1,570 variables / 422 constants — symbol density well above the 1-per-file soft bar.

Tests: 4 new extraction describe-blocks + detection/support assertions in __tests__/extraction.test.ts; full vitest suite passes locally (all pre-existing tests unaffected).

Not included (deliberately small)

• No kernel routing (stays on the wasm path, like the other recent language additions).
• No preload/load import-edge resolution to res:// paths (calls are captured; resolving them to file nodes would follow the Luau instance-path require pattern and can come as a follow-up).
• No README language-grid SVG icon (asset pipeline is maintainer-side).

---

Rebased onto main (post-1.6.0). The only conflict was CHANGELOG.md: the
GDScript entry now sits under ## [Unreleased] rather than inside the released
1.6.0 section. src/ merged without conflicts — 1.6.0's grammars.ts changes
(the C++ base-clause detection) don't touch the language-registration sites.
tsc clean, __tests__/extraction.test.ts passes in full (627 tests) on the
rebased tree.

🤖 Generated with Claude Code

[tiantian520tt]

it's wonderful. we need it, pls. thanks a lot!

[wakaru44]

How does this relate to the already ongoing GDScript PR's? #1098

[Plumvery]

Good question — short answer: #1098 is broader, this one is deliberately narrow.

• Add GDScript and Godot scene graph support #1098 (@i-snyder) — GDScript and Godot scene-graph (.tscn): 17 files, +1657.
• feat: add GDScript language support #1499 (@cosmicnag) — closest in scope: 5 files, +147.
• This PR — extraction only: 8 files, +226. The "Not included (deliberately
  small)" section above is the scope line: no kernel routing, no preload/load
  import-edge resolution, no scene parsing.

So against #1098 it's overlap rather than duplication — scene-graph support is real
work this PR doesn't attempt, and it could sit on top of whichever extractor lands.

Two things here that are independent of which one wins: the wasm is rebuilt from
upstream grammar source as ABI 15 and clears scripts/add-lang/check-grammar.mjs
(20/20 parses, heap-safe under multi-grammar reuse), and the var/const/signal
family needs a visitNode hook because those name their target through a
name-typed child the generic variable fallback can't read.

No attachment to this one landing over the others — happy to close it if #1098 or
#1499 goes in first. @colbymchenry's call.