Add mass unban: DELETE /api/bans/all clears all active bans

- Send fail2ban's `unban --all` command via new `unban_all_ips()` service
  function; returns the count of unbanned IPs
- Add `UnbanAllResponse` Pydantic model (message + count)
- Add `DELETE /api/bans/all` router endpoint; handles 502 on socket error
- Frontend: `bansAll` endpoint constant, `unbanAllBans()` API call,
  `UnbanAllResponse` type, `unbanAll` action in `useActiveBans` hook
- JailsPage: "Clear All Bans" button (visible when bans > 0) with a
  Fluent UI confirmation Dialog before executing the operation
- 7 new tests (3 service, 4 router); 440 total pass, 82% coverage

backend/app/routers/bans.py

@@ -5,6 +5,7 @@ Manual ban and unban operations and the active-bans overview:
 * ``GET    /api/bans/active`` — list all currently banned IPs
 * ``POST   /api/bans``        — ban an IP in a specific jail
 * ``DELETE /api/bans``        — unban an IP from one or all jails
+* ``DELETE /api/bans/all``    — unban every currently banned IP across all jails
 """
 
 from __future__ import annotations
@@ -17,7 +18,7 @@ if TYPE_CHECKING:
 from fastapi import APIRouter, HTTPException, Request, status
 
 from app.dependencies import AuthDep
-from app.models.ban import ActiveBanListResponse, BanRequest, UnbanRequest
+from app.models.ban import ActiveBanListResponse, BanRequest, UnbanAllResponse, UnbanRequest
 from app.models.jail import JailCommandResponse
 from app.services import geo_service, jail_service
 from app.services.jail_service import JailNotFoundError, JailOperationError
@@ -193,3 +194,39 @@ async def unban_ip(
         ) from exc
     except Fail2BanConnectionError as exc:
         raise _bad_gateway(exc) from exc
+
+
+@router.delete(
+    "/all",
+    response_model=UnbanAllResponse,
+    summary="Unban every currently banned IP across all jails",
+)
+async def unban_all(
+    request: Request,
+    _auth: AuthDep,
+) -> UnbanAllResponse:
+    """Remove all active bans from every fail2ban jail in a single operation.
+
+    Uses fail2ban's ``unban --all`` command to atomically clear every active
+    ban across all jails.  Returns the number of IPs that were unbanned.
+
+    Args:
+        request: Incoming request (used to access ``app.state``).
+        _auth: Validated session — enforces authentication.
+
+    Returns:
+        :class:`~app.models.ban.UnbanAllResponse` with the count of
+        unbanned IPs.
+
+    Raises:
+        HTTPException: 502 when fail2ban is unreachable.
+    """
+    socket_path: str = request.app.state.settings.fail2ban_socket
+    try:
+        count: int = await jail_service.unban_all_ips(socket_path)
+        return UnbanAllResponse(
+            message=f"All bans cleared. {count} IP address{'es' if count != 1 else ''} unbanned.",
+            count=count,
+        )
+    except Fail2BanConnectionError as exc:
+        raise _bad_gateway(exc) from exc