Refactor auth and setup services

- Updated auth_service.py to improve authentication logic
- Modified setup_service.py for better configuration handling
- Added comprehensive tests for setup_service
- Updated documentation in Tasks.md

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

Docs/Tasks.md

@@ -1,42 +1,3 @@
-## [Backend] Module-level imports inside dependency provider functions
-
-**Where found**
-
-- `backend/app/dependencies.py:151` — `from app.db import open_db` inside `get_db()`
-- `backend/app/dependencies.py:258, 270, 282, 294, 307, 319, 332` — local imports inside each `get_<repo>()` provider
-- Similar patterns in service provider functions
-
-**Why this is needed**
-
-FastAPI calls dependency provider functions on every request. While Python caches modules, the import statement still has overhead. More importantly, the pattern is inconsistent — some providers have module-level imports while others have local imports, making it unclear which providers are safe to call at high frequency.
-
-**Goal**
-
-Move all repository and service imports to module level in `dependencies.py`.
-
-**What to do**
-
-1. Move all repository imports to module level near the top
-2. Similarly move `from app.services import health_service` to module level
-3. Keep `from app.db import open_db` as local import (only needed within `get_db()`)
-4. Move `from app.services import auth_service` to module level with `TYPE_CHECKING` guard if circular deps prevent it
-
-**Possible traps and issues**
-
-- Moving imports to module level may expose hidden circular imports
-- Current local-import pattern was likely chosen to avoid circular deps — verify no circular dependencies before making change
-
-**Docs changes needed**
-
-- Update `Docs/Architekture.md` § 2.3 (Dependency Wiring) — repository and service imports should be at module level
-
-**Doc references**
-
-- `Docs/Architekture.md` § 2.3 (Dependency Wiring)
-- `backend/app/dependencies.py` (composition root)
-
----
-
 ## [Backend] `get_password_hash` lives in `setup_service` but is used by `auth_service`
 
 **Where found**