T-04: Encapsulate geo_service module-level mutable state in GeoCache class

Create GeoCache class with all mutable state as instance attributes:
- _cache, _neg_cache, _dirty, _geoip_reader, _geoip_initialized, _cache_lock
- All public methods: lookup(), lookup_batch(), lookup_cached_only(), flush_dirty(), load_from_db(), clear(), etc.

Initialization & Dependency Injection:
- Instantiate GeoCache in startup.py and store on app.state.geo_cache
- Add get_geo_cache() dependency function in dependencies.py
- Inject into routes and tasks via FastAPI's dependency system

Backward Compatibility:
- Maintain module-level functions in geo_service.py as deprecated wrappers
- All old callers continue to work through _default_geo_cache instance
- Remove test-escape-hatch functions (clear_cache, clear_neg_cache moved to methods)

Background Tasks:
- Update geo_cache_flush.py and geo_re_resolve.py to receive GeoCache instance
- Tasks now operate on injected instance rather than module globals

Tests:
- Refactor test_geo_service.py with geo_cache fixture providing fresh instances
- Update patch paths to target GeoCache methods correctly
- Fix internal state assertions to access instance attributes

Documentation:
- Update Architekture.md to document GeoCache as managed stateful service
- Describe cache lifecycle (load on startup, flush periodically, re-resolve stale)
- Note process-local limitations for multi-worker deployments

Fixes violation of Single Responsibility Principle: module no longer owns both
lookup logic and cache lifecycle management. Cache is now a first-class
injectable service with transparent lifecycle.

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

Docs/Architekture.md

@@ -196,7 +196,8 @@ The business logic layer. Services orchestrate operations, enforce rules, and co
 | `log_service.py` | Log preview and regex test operations (extracted from config_service) |
 | `history_service.py` | Queries the fail2ban database for historical ban records, builds per-IP timelines, computes ban counts and repeat-offender flags, and syncs new records into BanGUI's archive table |
 | `blocklist_service.py` | Downloads blocklists via aiohttp, validates IPs/CIDRs, applies bans through fail2ban or iptables, logs import results |
-| `geo_service.py` | Resolves IP addresses to country, ASN, and RIR using external APIs or a local database, caches results, and re-resolves unresolved geo cache entries |
+| `geo_cache.py` | **GeoCache** class that encapsulates all IP geolocation caching: resolves IP addresses to country, ASN, and organization using external APIs or a local MaxMind database, maintains in-memory and persistent caches with negative cache support, and manages background re-resolution. Instantiated once at startup and stored on `app.state.geo_cache` |
+| `geo_service.py` | (Deprecated) Backward-compatibility wrappers that delegate to the `GeoCache` instance. Kept for compatibility with existing code. New code should use `GeoCache` directly or via dependency injection |
 | `server_service.py` | Reads and writes fail2ban server-level settings (log level, log target, syslog socket, DB location, purge age) |
 | `health_service.py` | Probes fail2ban socket connectivity, retrieves server version and global stats, reports online/offline status |
 
@@ -667,6 +668,7 @@ BanGUI maintains its **own SQLite database** (separate from the fail2ban databas
 - The frontend `AuthProvider` checks session validity on mount and redirects to `/login` if invalid.
 - The backend `dependencies.py` provides an `authenticated` dependency that validates the session cookie on every protected endpoint.
 - **Session validation cache** — validated session tokens are cached in memory for 10 seconds (`_session_cache` dict in `dependencies.py`) to avoid a SQLite round-trip on every request from the same browser. The cache is invalidated immediately on logout. This cache is process-local and not safe for multi-worker or distributed deployments. A clustered deployment should replace `_session_cache` with a shared cache or remove it entirely.
+- **GeoCache** — `GeoCache` instance is created at startup and stored on `app.state.geo_cache`. It encapsulates all IP geolocation caching: in-memory lookup cache, negative cache for unresolvable IPs (with TTL), dirty set for persistence, and thread-safe async locking. Cache is loaded from the `geo_cache` SQLite table on startup. New resolutions are accumulated in memory and periodically flushed to the database by the `geo_cache_flush` background task. Stale entries are re-resolved by the `geo_re_resolve` task. Injected into routes and tasks via FastAPI's dependency system.
 - **Runtime state** — `RuntimeState` is process-local and only safe when BanGUI runs as a single asyncio worker. Mutating runtime state must not span `await` points because the current design relies on cooperative scheduling. Multi-worker or multi-process deployments must replace this runtime state with a shared coordination backend such as Redis, shared memory, or a database-backed store.
 - **Setup-completion flag** — once `is_setup_complete()` returns `True`, the result is stored in `app.state._setup_complete_cached`. The `SetupRedirectMiddleware` skips the DB query on all subsequent requests, removing 1 SQL query per request for the common post-setup case. The completion flag is only written after the runtime database is successfully initialized and all initial setup settings are persisted, preventing a failed setup from permanently bypassing the setup wizard.
 

Docs/Tasks.md

@@ -1,23 +1,3 @@
-### 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`
-
-**Why this is needed:** Four independent definitions can drift. The router default and service default are currently coincidentally aligned at 100, but nothing enforces this.
-
-**Goal:** Single definition in `app/utils/constants.py`, imported everywhere.
-
-**What to do:**
-1. Add `DEFAULT_PAGE_SIZE: Final[int] = 100` and `MAX_PAGE_SIZE: Final[int] = 500` to `app/utils/constants.py`.
-2. Replace all four local `_DEFAULT_PAGE_SIZE` and `_MAX_PAGE_SIZE` declarations with imports.
-
-**Possible traps and issues:** None significant. Pure search-and-replace.
-
-**Docs changes needed:** None.
-
-**Doc references:** `app/utils/constants.py`
-
----
-
 ### T-04 · Encapsulate `geo_service` module-level mutable state in a class
 
 **Where found:** `backend/app/services/geo_service.py` — module globals `_cache`, `_neg_cache`, `_dirty`, `_geoip_reader`, `_geoip_initialized`, `_cache_lock`