Refactor backend configuration and authentication

- Add comprehensive documentation for backend development
- Improve client IP detection with utility functions and tests
- Update auth router with better error handling
- Refactor config module with environment-based settings

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Docs/Tasks.md

@@ -1,22 +1,3 @@
-## 32) RateLimiter cleanup function is not scheduled/used
-- Where found:
-	- [backend/app/utils/rate_limiter.py](backend/app/utils/rate_limiter.py#L84)
-	- [backend/app/startup.py](backend/app/startup.py)
-- Why this is needed:
-	- Rate limiter state can grow over long runtimes.
-- Goal:
-	- Ensure periodic cleanup or bounded memory strategy.
-- What to do:
-	- Add scheduled cleanup or auto-eviction structure.
-- Possible traps and issues:
-	- Cleanup cadence too frequent can add overhead.
-- Docs changes needed:
-	- Add operational notes for auth throttling lifecycle.
-- Doc references:
-	- [backend/app/utils/rate_limiter.py](backend/app/utils/rate_limiter.py)
-
----
-
 ## 33) Trusted proxy configuration is hardcoded in auth router
 - Where found:
 	- [backend/app/routers/auth.py](backend/app/routers/auth.py#L46)