Chore/remove legacy root code

[VishakBaddur]

Description

Removes all confirmed-dead legacy code from before the api-service/ restructure, plus a second layer of legacy code found inside api-service/ itself that predates the LangGraph agent pipeline.

Two commits:

1. Removed the pre-restructure root-level codebase: config/, models/, controllers/, routes/, services/, db_update/, templates/, static/, root app.py, root requirements.txt. Confirmed not copied into any Docker image, not imported anywhere in api-service/, ingestion-service/, or notification-service/.
2. Removed the old NewsController/NewsService route system still living inside api-service/: 5 routes, their templates, llm_config.json. This was carried into api-service/ during the restructure but is no longer used; the LangGraph pipeline now handles /chat, /dashboard, /sources, and /subscribe. Also fixed the 404 handler, which depended on state only the old routes ever set, it would have crashed on any blueprint-level 404 once this code was gone.

Related Issue

Part of #244 (final submission wrap-up)

Motivation and Context

Cleaning up dead code before final GSoC submission so the repo only reflects what's actually built and running, not scaffolding from before the restructure.

How Has This Been Tested?

Confirmed via grep that nothing in any active service imports from the deleted paths. Checked all three services' Docker build contexts are scoped to their own subdirectories, so the root-level code was never even shipped. Full api-service test suite: 148/148 passing before and after both commits. Verified live via docker-compose: app boots with no import errors, /, /dashboard, /sources all return 200, dashboard renders with no template errors, and the fixed 404 handler works for the case it's actually reachable for.

Screenshots (if appropriate):

N/A, no UI changes, cleanup only.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.