Refactor backend services and routers

- Reorganized dashboard router with improved structure
- Enhanced ban_service with better separation of concerns
- Updated history service with cleaner logic
- Improved constants and configuration handling
- Updated documentation of completed tasks

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

Docs/Tasks.md

@@ -1,28 +1,3 @@
-### T-02 · Remove duplicate router-level exception helpers — use global handlers only
-
-**Where found:** `backend/app/routers/jails.py`, `bans.py`, `jail_config.py`, `server.py`, `config_misc.py` each define `_bad_gateway()`, `_not_found()`, `_conflict()`. Global handlers for the same exceptions exist in `backend/app/main.py`.
-
-**Why this is needed:** Two parallel error-mapping systems produce inconsistent error bodies. A `Fail2BanConnectionError` caught by a router produces `"Cannot reach fail2ban: {exc}"` while one that escapes produces `"{exc}"` (just the exception string). Adds dead code and maintenance burden.
-
-**Goal:** All domain exceptions propagate to the global handlers in `main.py`. Routers contain zero HTTP error construction.
-
-**What to do:**
-1. Remove all `_bad_gateway`, `_not_found`, `_conflict` helpers from routers.
-2. Remove the `try/except` blocks in router handlers that convert domain exceptions to `HTTPException` — let them propagate.
-3. Verify that all domain exception types are covered in `main.py`'s `add_exception_handler` registrations.
-4. Confirm error body format is consistent across all affected endpoints.
-
-**Possible traps and issues:**
-- A few routers catch `ValueError` from service layer and re-raise as `JailOperationError` — ensure those paths still reach the correct global handler.
-- FastAPI evaluates exception handlers in registration order. Verify the order in `create_app` is most-specific first.
-- Integration tests that assert on specific error message strings may need updates.
-
-**Docs changes needed:** `Docs/Backend-Development.md` — document that routers must not construct `HTTPException` for domain errors; they should raise or let domain exceptions propagate.
-
-**Doc references:** `Docs/Backend-Development.md`
-
----
-
 ### T-03 · Centralise `_DEFAULT_PAGE_SIZE` constant
 
 **Where found:** `backend/app/routers/dashboard.py:45`, `routers/history.py:34`, `services/ban_service.py:70`, `services/history_service.py:49`