feat(rag): add local retrieval pipeline and search tooling

[aleygey]

Issue for this PR

Closes #

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This PR adds a local RAG pipeline and retrieval toolchain.

Changes included in this PR:

• add .opencode/tool/rag_search.ts
• add .opencode/plugins/rag_context.ts for automatic context injection
• add shared RAG helpers in .opencode/rag.ts
• add bootstrap/init/update scripts under script/rag
• add retrieval/debug utilities and requirement files
• add a rag-pipeline skill
• add supporting docs in specs/

Why this works:

• rag_search provides a consistent tool entrypoint for retrieval
• the plugin injects retrieval state into the chat flow
• the scripts make index creation and incremental updates reproducible
• the docs describe the intended pipeline and runtime behavior

How did you verify your code works?

I reviewed the command wiring, paths, and config integration locally.
I did not run a full end-to-end retrieval pipeline against a live vector DB in this environment.

Screenshots / recordings

N/A

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR