Expose usedns, date_pattern, and prefregex in jail config UI

- Add use_dns and prefregex fields to JailConfig model (backend + frontend types)
- Add prefregex to JailConfigUpdate; validate as regex before writing
- Fetch usedns and prefregex in get_jail_config via asyncio.gather
- Write usedns and prefregex in update_jail_config
- ConfigPage JailAccordionPanel: editable date_pattern input, dns_mode
  Select dropdown (yes/warn/no/raw), and prefregex input
- 8 new service unit tests + 3 new router integration tests
- 628 tests pass; 85% line coverage; ruff/mypy/tsc/eslint clean

backend/tests/test_routers/test_config.py

@@ -77,6 +77,8 @@ def _make_jail_config(name: str = "sshd") -> JailConfig:
         date_pattern=None,
         log_encoding="UTF-8",
         backend="polling",
+        use_dns="warn",
+        prefregex="",
         actions=["iptables"],
     )
 
@@ -234,6 +236,45 @@ class TestUpdateJailConfig:
 
         assert resp.status_code == 400
 
+    async def test_204_with_dns_mode(self, config_client: AsyncClient) -> None:
+        """PUT /api/config/jails/sshd accepts dns_mode field."""
+        with patch(
+            "app.routers.config.config_service.update_jail_config",
+            AsyncMock(return_value=None),
+        ):
+            resp = await config_client.put(
+                "/api/config/jails/sshd",
+                json={"dns_mode": "no"},
+            )
+
+        assert resp.status_code == 204
+
+    async def test_204_with_prefregex(self, config_client: AsyncClient) -> None:
+        """PUT /api/config/jails/sshd accepts prefregex field."""
+        with patch(
+            "app.routers.config.config_service.update_jail_config",
+            AsyncMock(return_value=None),
+        ):
+            resp = await config_client.put(
+                "/api/config/jails/sshd",
+                json={"prefregex": r"^%(__prefix_line)s"},
+            )
+
+        assert resp.status_code == 204
+
+    async def test_204_with_date_pattern(self, config_client: AsyncClient) -> None:
+        """PUT /api/config/jails/sshd accepts date_pattern field."""
+        with patch(
+            "app.routers.config.config_service.update_jail_config",
+            AsyncMock(return_value=None),
+        ):
+            resp = await config_client.put(
+                "/api/config/jails/sshd",
+                json={"date_pattern": "%Y-%m-%d %H:%M:%S"},
+            )
+
+        assert resp.status_code == 204
+
 
 # ---------------------------------------------------------------------------
 # GET /api/config/global