Add database migration 5: Indexes for history_archive query performance

- Add composite index on (jail, timeofban DESC) for dashboard filtering
- Add composite index on (timeofban DESC, jail, action) for time-range queries
- Add single-column indexes on ip and action for targeted filtering
- Update schema version to 5 and document in Backend-Development.md

Indexes optimize common dashboard and API query patterns with pagination.

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

Docs/Tasks.md

@@ -1,21 +1,3 @@
-## 37) Multi-worker safety check depends on one environment variable
-- Where found:
-	- [backend/app/startup.py](backend/app/startup.py#L61)
-- Why this is needed:
-	- Other process managers can still launch multiple workers without this variable.
-- Goal:
-	- Enforce scheduler single-executor safety regardless of launcher.
-- What to do:
-	- Add robust single-run lock/leader mechanism for scheduler ownership.
-- Possible traps and issues:
-	- Locking strategy must be reliable in container orchestration.
-- Docs changes needed:
-	- Expand deployment constraints and supported run modes.
-- Doc references:
-	- [Docs/Architekture.md](Docs/Architekture.md)
-
----
-
 ## 38) History archive query paths may need explicit indexing plan
 - Where found:
 	- [backend/app/db.py](backend/app/db.py)