fix(rag): escape $ in GraphRAG file_pattern, fix cache type

[AmirF194]

GraphRAG's load_config() treats the whole settings.yaml text as a string.Template and substitutes env vars into it before parsing YAML. Our generated file_pattern regex, .*\.txt$, contains a bare $, which is an invalid placeholder to that pass and raises ValueError: Invalid placeholder in string, before indexing can even start.

Once that is escaped, the next call to fail is graphrag_cache.CacheFactory.create_cache (invoked from GraphRAG's own run_pipeline.py): our cache.type was set to "file", but "file" is a storage type, not a registered cache type. GraphRAG's CacheFactory only registers json/memory/none, so the first indexing run raises ValueError: CacheConfig.type 'file' is not registered in the CacheFactory.

Fix

In deeptutor/services/rag/pipelines/graphrag/config.py:

• file_pattern: .*\.txt$ → .*\.txt$$ (escapes the literal $ for string.Template).
• cache.type: "file" → "json" (the storage type stays "file"; only the cache backend id was wrong).

Verification

Installed graphrag==3.1.1 (the version this repo pins) in a clean Docker container and drove the real path: write_settings() → graphrag.config.load_config.load_config() → graphrag_cache.cache_factory.create_cache(), the same call graphrag/index/run/run_pipeline.py:45 makes. Both errors reproduce verbatim on unpatched config.py; both are gone after the fix, and create_cache returns a real JsonCache.

Added a regression test in tests/services/rag/test_graphrag_pipeline.py that exercises this same real path, guarded with pytest.importorskip("graphrag") since the package is not installed in this repo's CI (per the test module's own docstring). Ran it RED against the unpatched file and GREEN after the fix, both with graphrag installed; also ran the full existing test file and the full tests/ suite with graphrag uninstalled (matching CI) to confirm no regressions: 2573 passed, 8 skipped, 3 pre-existing failures unrelated to this change (missing git binary in the minimal container, confirmed by installing it). ruff check and ruff format --check (0.16.0, matching CI's lint job) are clean on both changed files.

Did not reproduce or address the issue's third symptom (uvloop/nest_asyncio event-loop clash) since it is an orthogonal event-loop policy issue, not a config-generation bug, and is not required to fix these two.

Fixes #695