feat: add Objective-C language support

[0x1306a94]

Summary

Adds partial Objective-C support to the tree-sitter extraction pipeline so iOS/macOS codebases can be indexed with the same graph queries as other languages.

Wiring

• Register objc in LANGUAGES, WASM_GRAMMAR_FILES (tree-sitter-objc.wasm from tree-sitter-wasms, ABI 14), and EXTRACTORS
• Map .m / .mm → objc; classify .h as Objective-C when content matches @interface / @implementation / @protocol / @synthesize (after the existing C++ .h heuristic)
• File discovery uses zero-config isSourceFile + .gitignore — no separate include globs needed

Extraction (objc.ts)

• Classes — @interface emits one class node; @implementation reuses it via visitNode (avoids duplicate class/method nodes)
• Protocols — @protocol → protocol nodes
• Methods — method_definition only; full multi-part selectors (doThing:with:) via resolveName
• Properties — @property via extractPropertyName (walks struct_declarator / pointer_declarator)
• Functions & imports — C-style function_definition and #import (preproc_include)
• Inheritance — extends for superclass; implements for angle-bracket protocols on @interface
• Calls — call_expression and [receiver message] (message_expression) call edges

Core hooks

• resolveName / extractPropertyName on LanguageExtractor (used by ObjC; generic fallbacks unchanged)
• extractInheritance early-return branch for class_interface
• Import resolver try-order: .h, .m, .mm

Docs & eval corpus

• README: Partial support row (not full — documents .mm ObjC++ limits)
• CHANGELOG [Unreleased] entry with known limitations
• Agent-eval corpus: Masonry (small), FMDB (medium), SDWebImage (large)

Benchmark (local dev build)

Repo	Files	Nodes	verify-extraction	Notes
Masonry	267	1,418	PASS	A/B: 6 tool calls / 1 Read vs 18 / 15 Reads
FMDB	~80	—	PASS
SDWebImage	274	3,710	PASS

Known limitations

• Chained/nested message sends (e.g. [[Class alloc] init]) only record the innermost method name
• No instantiates edge for [Class alloc] patterns
• @protocol Foo <Bar> refinement lists not yet wired to implements edges
• Heavy C++ in .mm files may parse incompletely under the ObjC grammar

Test plan

• npm run build
• npx vitest run __tests__/extraction.test.ts -t "Objective-C" (7 tests)
• node scripts/add-lang/verify-extraction.mjs on sample + Masonry / FMDB / SDWebImage