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_services/test_config_service.py

@@ -75,6 +75,8 @@ _DEFAULT_JAIL_RESPONSES: dict[str, Any] = {
     "get|sshd|datepattern": (0, None),
     "get|sshd|logencoding": (0, "UTF-8"),
     "get|sshd|backend": (0, "polling"),
+    "get|sshd|usedns": (0, "warn"),
+    "get|sshd|prefregex": (0, ""),
     "get|sshd|actions": (0, ["iptables"]),
 }
 
@@ -143,6 +145,41 @@ class TestGetJailConfig:
 
         assert result.jail.date_pattern is None
 
+    async def test_use_dns_populated(self) -> None:
+        """get_jail_config returns use_dns from the socket response."""
+        responses = {**_DEFAULT_JAIL_RESPONSES, "get|sshd|usedns": (0, "no")}
+        with _patch_client(responses):
+            result = await config_service.get_jail_config(_SOCKET, "sshd")
+
+        assert result.jail.use_dns == "no"
+
+    async def test_use_dns_default_when_missing(self) -> None:
+        """get_jail_config defaults use_dns to 'warn' when socket returns None."""
+        responses = {**_DEFAULT_JAIL_RESPONSES, "get|sshd|usedns": (0, None)}
+        with _patch_client(responses):
+            result = await config_service.get_jail_config(_SOCKET, "sshd")
+
+        assert result.jail.use_dns == "warn"
+
+    async def test_prefregex_populated(self) -> None:
+        """get_jail_config returns prefregex from the socket response."""
+        responses = {
+            **_DEFAULT_JAIL_RESPONSES,
+            "get|sshd|prefregex": (0, r"^%(__prefix_line)s"),
+        }
+        with _patch_client(responses):
+            result = await config_service.get_jail_config(_SOCKET, "sshd")
+
+        assert result.jail.prefregex == r"^%(__prefix_line)s"
+
+    async def test_prefregex_empty_when_missing(self) -> None:
+        """get_jail_config returns empty string prefregex when socket returns None."""
+        responses = {**_DEFAULT_JAIL_RESPONSES, "get|sshd|prefregex": (0, None)}
+        with _patch_client(responses):
+            result = await config_service.get_jail_config(_SOCKET, "sshd")
+
+        assert result.jail.prefregex == ""
+
 
 # ---------------------------------------------------------------------------
 # list_jail_configs
@@ -275,6 +312,88 @@ class TestUpdateJailConfig:
         assert add_cmd is not None
         assert add_cmd[3] == "new_pattern"
 
+    async def test_sets_dns_mode(self) -> None:
+        """update_jail_config sends 'set <jail> usedns' for dns_mode."""
+        from app.models.config import JailConfigUpdate
+
+        sent_commands: list[list[Any]] = []
+
+        async def _send(command: list[Any]) -> Any:
+            sent_commands.append(command)
+            return (0, "OK")
+
+        class _FakeClient:
+            def __init__(self, **_kw: Any) -> None:
+                self.send = AsyncMock(side_effect=_send)
+
+        update = JailConfigUpdate(dns_mode="no")
+        with patch("app.services.config_service.Fail2BanClient", _FakeClient):
+            await config_service.update_jail_config(_SOCKET, "sshd", update)
+
+        usedns_cmd = next(
+            (c for c in sent_commands if len(c) >= 4 and c[2] == "usedns"),
+            None,
+        )
+        assert usedns_cmd is not None
+        assert usedns_cmd[3] == "no"
+
+    async def test_sets_prefregex(self) -> None:
+        """update_jail_config sends 'set <jail> prefregex' for prefregex."""
+        from app.models.config import JailConfigUpdate
+
+        sent_commands: list[list[Any]] = []
+
+        async def _send(command: list[Any]) -> Any:
+            sent_commands.append(command)
+            return (0, "OK")
+
+        class _FakeClient:
+            def __init__(self, **_kw: Any) -> None:
+                self.send = AsyncMock(side_effect=_send)
+
+        update = JailConfigUpdate(prefregex=r"^%(__prefix_line)s")
+        with patch("app.services.config_service.Fail2BanClient", _FakeClient):
+            await config_service.update_jail_config(_SOCKET, "sshd", update)
+
+        prefregex_cmd = next(
+            (c for c in sent_commands if len(c) >= 4 and c[2] == "prefregex"),
+            None,
+        )
+        assert prefregex_cmd is not None
+        assert prefregex_cmd[3] == r"^%(__prefix_line)s"
+
+    async def test_skips_none_prefregex(self) -> None:
+        """update_jail_config does not send prefregex command when field is None."""
+        from app.models.config import JailConfigUpdate
+
+        sent_commands: list[list[Any]] = []
+
+        async def _send(command: list[Any]) -> Any:
+            sent_commands.append(command)
+            return (0, "OK")
+
+        class _FakeClient:
+            def __init__(self, **_kw: Any) -> None:
+                self.send = AsyncMock(side_effect=_send)
+
+        update = JailConfigUpdate(prefregex=None)
+        with patch("app.services.config_service.Fail2BanClient", _FakeClient):
+            await config_service.update_jail_config(_SOCKET, "sshd", update)
+
+        prefregex_cmd = next(
+            (c for c in sent_commands if len(c) >= 4 and c[2] == "prefregex"),
+            None,
+        )
+        assert prefregex_cmd is None
+
+    async def test_raises_validation_error_on_invalid_prefregex(self) -> None:
+        """update_jail_config raises ConfigValidationError for an invalid prefregex."""
+        from app.models.config import JailConfigUpdate
+
+        update = JailConfigUpdate(prefregex="[invalid")
+        with pytest.raises(ConfigValidationError, match="prefregex"):
+            await config_service.update_jail_config(_SOCKET, "sshd", update)
+
 
 # ---------------------------------------------------------------------------
 # get_global_config