Fix backend unable to open fail2ban database in dev compose

The backend container mounted fail2ban-dev-config as an anonymous named
volume, while the fail2ban container used a bind-mount of the same local
directory. The backend's /config was therefore always empty, causing
sqlite3.OperationalError when ban_service attempted to open the path
returned by 'get dbfile' (/config/fail2ban/fail2ban.sqlite3).

Change the backend volume declaration from the named volume reference
to the same bind-mount used by fail2ban:
  fail2ban-dev-config:/config:ro  →  ./fail2ban-dev-config:/config:ro

Also removes the now-unused 'fail2ban-dev-config' named-volume entry.

Affected endpoints (all returned HTTP 500, now return HTTP 200):
  GET /api/dashboard/bans
  GET /api/dashboard/accesses
  GET /api/dashboard/bans/by-country

Docker/compose.debug.yml

@@ -65,7 +65,7 @@ services:
       - ../fail2ban-master:/app/fail2ban-master:ro,z
       - bangui-dev-data:/data
       - fail2ban-dev-run:/var/run/fail2ban:ro
-      - fail2ban-dev-config:/config:ro
+      - ./fail2ban-dev-config:/config:ro
     ports:
       - "${BANGUI_BACKEND_PORT:-8000}:8000"
     command:
@@ -114,8 +114,6 @@ volumes:
     driver: local
   frontend-node-modules:
     driver: local
-  fail2ban-dev-config:
-    driver: local
   fail2ban-dev-run:
     driver: local