feat(core): Go scanner - registry integration and 90%+ test coverage

[prosdev]

Summary

Complete Go scanner integration into the scanner registry with comprehensive test coverage and production hardening.

Background

Part of Epic #128: Go Language Support
Depends on: #129 (Core Scanner), #130 (Methods & Generics)

Tasks

Registry Integration

• Register GoScanner in createDefaultRegistry()
• Add .go to supported extensions list
• Update scanner auto-detection logic
• Export from packages/core/src/scanner/index.ts

Generated File Handling

• Skip files starting with // Code generated
• Skip vendor/ directory
• Skip common build artifacts (bin/, dist/)
• Add isGenerated detection helper

Test Coverage (Target: 90%+)

• Unit tests for all extraction types
• Edge cases: empty files, syntax errors, partial files
• Generated file skip logic tests
• Integration test with realistic Go project structure
• Test file detection (*_test.go → isTest: true)

Documentation

• Update packages/core/src/scanner/README.md with Go section
• Add Go input/output examples
• Document supported constructs table
• Add troubleshooting notes

Edge Cases

• Handle build tags: //go:build linux
• Handle blank identifiers: var _ Interface = (*Impl)(nil)
• Handle init functions: func init() {}
• Handle embedded structs
• Handle multiple declarations: var a, b, c int

Acceptance Criteria

• Go scanner registered in default registry
• dev index . works on Go repositories out of the box
• Generated files (.gen.go, .pb.go) are skipped
• Test coverage ≥ 90% (matching TypeScript scanner)
• README updated with Go documentation
• All edge cases handled gracefully (no crashes)

Test File Structure

packages/core/src/scanner/
├── go.ts                    # GoScanner implementation
├── go.test.ts               # Comprehensive test suite
├── __fixtures__/
│   └── go/
│       ├── simple.go        # Basic functions, structs
│       ├── methods.go       # Receiver methods
│       ├── generics.go      # Generic types and functions
│       ├── generated.go     # Should be skipped
│       └── edge-cases.go    # Build tags, init, embedded

References

• TypeScript scanner coverage: 94.94%
• Scanner test patterns: packages/core/src/scanner/scanner.test.ts