Codebase cleanup: deduplicate, remove dead code, fix structure

[nv78]

Summary

Language endpoints (~500 lines → thin wrappers)

• Extracted shared extract_text_from_file() and all chat handler logic into a single language_chat.py with a make_language_blueprint() factory
• Each language file (arabic, spanish, chinese, japanese, korean, gtm) is now a one-liner that passes its model ID, system prompt, and language-specific strings to the factory
• Eliminates ~500 lines of copy-paste code

financeGPT/chatbot_endpoints.py

• Removed 18 pass-through wrapper functions (e.g. add_message_to_db, retrieve_chats_from_db) that did nothing but delegate to database.db
• Replaced with direct re-export aliases — same public API, zero redundant code
• Removed unused service function re-assignments that were never consumed within the module

Dead code removed from app.py

• /process-message-pdf-demo, /ingest-pdf-demo, /download-chat-history-demo endpoints and their global state
• Commented-out /reset-chat-demo block
• /temp-test development endpoint
• Stale TODO: COMMENT OUT WHEN DEPLOY TO PROD comment

Package structure

• Added missing __init__.py to 13 backend packages so they are importable as proper Python packages

Docker

• backend/Dockerfile: combined two separate apt-get RUN layers into one (fewer image layers, faster builds), removed redundant separate pip install tokenizers anthropic step, upgraded to python:3.12-slim
• frontend/Dockerfile: removed npm install --force (no longer needed), upgraded to node:22-alpine

Redux

• Removed unused lastFetchTime state and selectLastFetchTime selector from ChatSlice

Test plan

• docker compose up --build succeeds with new Dockerfiles
• All 5 language chat endpoints respond correctly (/api/chat/arabic, /api/chat/spanish, etc.)
• CI passes: Ruff lint, MyPy, pytest (≥92% coverage), frontend build

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