Add broader file support and folder indexing

[coloboxp]

Summary:

• Add support for Office files, source code, and config files
• Add folder indexing (Downloads, Documents, Desktop, and custom folders)
• Add custom reader config and a sample reader
• Add persisted index option and update docs/changelog

Credits:

• Upstream PR Persisted indices jonfairbanks/local-rag#57 (persisted indices)
• Upstream PR Enhance streamlit/config.toml with SSL capabilities jonfairbanks/local-rag#67 (Streamlit SSL config comments)
• Upstream PR Bump the pip group across 1 directory with 3 updates jonfairbanks/local-rag#64 (dependency bump) superseded by broader dependency updates in this PR

Demo:

• Open "Local Files" → check Downloads/Documents/Desktop
• Add a custom folder
• Upload .docx/.pptx/.xlsx and click Process

Testing:

• pipenv sync
• pipenv run python -m py_compile components/tabs/local_files.py components/page_state.py utils/llama_index.py utils/rag_pipeline.py utils/file_readers.py utils/readers/sample_reader.py
• Streamlit headless boot smoke test
• Ingestion smoke test with .txt/.json/.yaml/.ini/.py/.docx/.pptx/.xlsx