Fix geo cache write performance: batch commits, read-only GETs, dirty flush

- Remove per-IP db.commit() from _persist_entry() and _persist_neg_entry();
  add a single commit after the full lookup_batch() chunk loop instead.
  Reduces commits from ~5,200 to 1 per bans/by-country request.

- Remove db dependency from GET /api/dashboard/bans and
  GET /api/dashboard/bans/by-country; pass app_db=None so no SQLite
  writes occur during read-only requests.

- Add _dirty set to geo_service; _store() marks resolved IPs dirty.
  New flush_dirty(db) batch-upserts all dirty entries in one transaction.
  New geo_cache_flush APScheduler task flushes every 60 s so geo data
  is persisted without blocking requests.

backend/app/routers/dashboard.py

@@ -9,16 +9,14 @@ Also provides ``GET /api/dashboard/bans`` for the dashboard ban-list table.
 
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Annotated
-
-import aiosqlite
+from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
     import aiohttp
 
-from fastapi import APIRouter, Depends, Query, Request
+from fastapi import APIRouter, Query, Request
 
-from app.dependencies import AuthDep, get_db
+from app.dependencies import AuthDep
 from app.models.ban import (
     BanOrigin,
     BansByCountryResponse,
@@ -77,7 +75,6 @@ async def get_server_status(
 async def get_dashboard_bans(
     request: Request,
     _auth: AuthDep,
-    db: Annotated[aiosqlite.Connection, Depends(get_db)],
     range: TimeRange = Query(default=_DEFAULT_RANGE, description="Time-range preset."),
     page: int = Query(default=1, ge=1, description="1-based page number."),
     page_size: int = Query(default=_DEFAULT_PAGE_SIZE, ge=1, le=500, description="Items per page."),
@@ -90,12 +87,13 @@ async def get_dashboard_bans(
 
     Reads from the fail2ban database and enriches each entry with
     geolocation data (country, ASN, organisation) from the ip-api.com
-    free API.  Results are sorted newest-first.
+    free API.  Results are sorted newest-first.  Geo lookups are served
+    from the in-memory cache only; no database writes occur during this
+    GET request.
 
     Args:
         request: The incoming request (used to access ``app.state``).
         _auth: Validated session dependency.
-        db: BanGUI application database (for persistent geo cache writes).
         range: Time-range preset — ``"24h"``, ``"7d"``, ``"30d"``, or
             ``"365d"``.
         page: 1-based page number.
@@ -115,7 +113,7 @@ async def get_dashboard_bans(
         page=page,
         page_size=page_size,
         http_session=http_session,
-        app_db=db,
+        app_db=None,
         origin=origin,
     )
 
@@ -128,7 +126,6 @@ async def get_dashboard_bans(
 async def get_bans_by_country(
     request: Request,
     _auth: AuthDep,
-    db: Annotated[aiosqlite.Connection, Depends(get_db)],
     range: TimeRange = Query(default=_DEFAULT_RANGE, description="Time-range preset."),
     origin: BanOrigin | None = Query(
         default=None,
@@ -139,12 +136,13 @@ async def get_bans_by_country(
 
     Uses SQL aggregation (``GROUP BY ip``) and batch geo-resolution to handle
     10 000+ banned IPs efficiently.  Returns a ``{country_code: count}`` map
-    and the 200 most recent raw ban rows for the companion access table.
+    and the 200 most recent raw ban rows for the companion access table.  Geo
+    lookups are served from the in-memory cache only; no database writes occur
+    during this GET request.
 
     Args:
         request: The incoming request.
         _auth: Validated session dependency.
-        db: BanGUI application database (for persistent geo cache writes).
         range: Time-range preset.
         origin: Optional filter by ban origin.
 
@@ -159,7 +157,7 @@ async def get_bans_by_country(
         socket_path,
         range,
         http_session=http_session,
-        app_db=db,
+        app_db=None,
         origin=origin,
     )