Add support for Go language parsing

[amaar-mc]

Wit currently supports TypeScript/JavaScript and Python via Tree-sitter WASM grammars. Go is one of the most requested languages for AI coding agents.

What needs to happen:

• Add tree-sitter-go.wasm from tree-sitter-wasms package
• Extend createParserService() in src/parser/loader.ts to load the Go grammar
• Add Go symbol extraction in src/parser/symbols.ts (function declarations, type declarations, method declarations)
• Add Go call edge extraction in src/parser/calls.ts
• Tests for all of the above

The architecture is already extensible — this is mostly following the existing TypeScript/Python pattern.