feat(zig): add Zig 0.16+ language support

[guysenpai]

Summary

• Adds Zig language support (Zig 0.16+) via tree-sitter-zig, indexing .zig and .zon files
• Extracts: top-level functions, struct declarations + methods, enums + members, error sets (as enums), @import (as import nodes with unresolved imports references), pub visibility, plain constants/variables, and test "..." { ... } blocks (as functions)
• Adds **/*.zig and **/*.zon to DEFAULT_CONFIG.include so the scanner picks them up out of the box

Implementation notes

• New extractor: src/extraction/languages/zig.ts (modelled after rust.ts)
• Registered in src/extraction/languages/index.ts
• zig added to LANGUAGES const in src/types.ts
• WASM grammar wired via tree-sitter-wasms package (no local wasm file needed)
• Struct methods are classified automatically via the existing isInsideClassLikeNode() scope-stack mechanism in tree-sitter.ts — no changes to core extractors
• Zig's parameters AST node has no field name, so getSignature finds it by type instead of getChildByField
• pub is an anonymous token in the tree-sitter-zig grammar — detected by iterating children

Known limitation (documented in code + CHANGELOG)

Comptime-generated types like fn Physics(comptime R: type) type { return struct { ... }; } are not resolvable at the tree-sitter level (would require full type inference). Methods on such types are not extracted.

Test plan

• 12 new tests in __tests__/extraction.test.ts under describe('Zig Extraction', ...) covering: function declarations (pub/private), signatures, structs + fields, struct methods + containment, enums + members, error sets, @import (simple + chained), constants/variables, test blocks, function calls
• npm run test → 531/531 pass (with GIT_CONFIG_KEY_0=commit.gpgsign GIT_CONFIG_VALUE_0=false to bypass the unrelated test-env GPG signing failures)
• npm run build → clean
• Indexed real Zig fixtures: ≥10 fn/struct/enum nodes + ≥1 calls edge between Zig nodes

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Generated by Claude Code