Documentation: language adapters guide (docs/language-adapters-guide.md)

[Dimwiddle]

Summary

Add docs/language-adapters-guide.md — a step-by-step guide for adding new language support (grammars, miners, framework detection) to the discovery pipeline.

Depends on: #124, #125, #126

Content

The guide has been drafted and committed to the repo. It covers:

1. Registering a new SupportedLanguage enum member
2. Adding the tree-sitter grammar package and loader
3. Extending FrameworkDetector for the new language
4. Creating miners (test functions, API routes) with MinerContext and typed metadata
5. Registering miners in build_default_pipeline()
6. Test fixture strategy
7. Full checklist for new adapters
8. MinerContext reference table
9. Configuration via pyproject.toml
10. Future enhancements (entry points, shared conftest, caching, traceability decoupling)

Uses Go as the running example throughout.

File

docs/language-adapters-guide.md (already drafted in repo)

Acceptance criteria

• Guide is technically accurate against the implemented discovery pipeline APIs
• All code examples compile/validate against the actual models (Discovery: DiscoveredItem data models and pipeline contracts #124) and protocol (Discovery: pipeline orchestrator #126)
• MinerContext reference matches the implemented context.py
• Typed metadata examples match TestFunctionMeta, ApiRouteMeta from Discovery: DiscoveredItem data models and pipeline contracts #124
• Linked from docs/index.md under a new "Extending SpecLeft" section
• Reviewed for consistency with existing docs style (docs/spec-format.md, docs/agent-contract.md)