Support markdown and plain-text file ingestion in the RAG pipeline

[alimaandev]

Task

\core/rag.py\ currently ingests plain strings via \ingest_document. Issue #22 asked for PDF/txt/markdown file ingestion; the RAG plugin (\plugins/builtins/rag_plugin.py) is text-only today.

Do

1. Extend \ingest_document\ to accept a \source\ type, or add a helper to read local files
2. Add markdown handling (strip code fences/headings as needed) and .txt\ support
3. Wire it into the \ingest_document\ tool / API so users can pass a file path
4. Add tests in \ ests/test_rag.py\ (mirror the existing tmp_path-isolated pattern)

Verify

• \python -m pytest tests/test_rag.py -q\ passes
• Ingesting a small .md\ file returns sensible chunks
• 
  uff check .\ clean

Notes

• PDF is harder (needs an extra lib) — markdown + txt is the core scope; note PDF as future work.
• Use \�syncio.to_thread\ for file reads per project conventions.

[kaminimangal]

@alimaandev can I take this? I'll add file path support to ingest_document, handle md/txt, and add tests in test_rag.py. Assign me please!

[alimaandev]

Assigned! Thanks @kaminimangal. When you open a PR, CI will run Backend (Python) + Frontend (TypeScript) checks automatically. Looking forward to it.