refactor(backend): clean up jail service, add error handling service

- Extract jail status/processing to helper functions
- Add error_handling.py service for centralized error handling
- Update config.py with validation and defaults
- Update .env.example with all config options
- Remove obsolete Tasks.md, add Service-Development.md
- Minor fixes across routers and services

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

backend/.env.example

@@ -31,3 +31,16 @@ BANGUI_LOG_LEVEL=info
 # from a different origin than the backend.
 # Leave this blank in production when the UI is served from the same origin.
 BANGUI_CORS_ALLOWED_ORIGINS=http://localhost:5173
+
+# ---------------------------------------------------------------------------
+# Pagination & display limits
+# ---------------------------------------------------------------------------
+
+# Maximum records per paginated response. Must be between 1 and 10000.
+BANGUI_MAX_PAGE_SIZE=500
+
+# Maximum IP lines returned in a blocklist source preview. Must be at least 1.
+BANGUI_PREVIEW_MAX_LINES=100
+
+# Number of days to retain historical ban records before archival cleanup.
+BANGUI_HISTORY_RETENTION_DAYS=90