Add filter write/create/delete and jail-filter assign endpoints (Task 2.2)

- PUT /api/config/filters/{name}: updates failregex/ignoreregex/datepattern/
  journalmatch in filter.d/{name}.local; validates regex via re.compile();
  supports ?reload=true
- POST /api/config/filters: creates filter.d/{name}.local from FilterCreateRequest;
  returns 409 if file already exists
- DELETE /api/config/filters/{name}: deletes .local only; returns 409 for
  conf-only (readonly) filters
- POST /api/config/jails/{name}/filter: assigns filter to jail by writing
  'filter = {name}' to jail.d/{jail}.local; supports ?reload=true
- New models: FilterUpdateRequest, FilterCreateRequest, AssignFilterRequest
- New service helpers: _safe_filter_name, _validate_regex_patterns,
  _write_filter_local_sync, _set_jail_local_key_sync
- Fixed .local-only filter discovery in _parse_filters_sync (5-tuple return)
- Fixed get_filter extension stripping (.local is 6 chars not 5)
- Renamed file_config.py raw-write routes to /raw suffix
  (PUT /filters/{name}/raw, POST /filters/raw) to avoid routing conflicts
- Full service + router tests; all 930 tests pass

backend/app/routers/file_config.py

@@ -9,8 +9,8 @@ Endpoints:
 * ``PUT  /api/config/jail-files/{filename}``        — overwrite a jail config file
 * ``PUT  /api/config/jail-files/{filename}/enabled`` — enable/disable a jail config
 * ``GET  /api/config/filters/{name}/raw``          — get one filter file raw content
-* ``PUT  /api/config/filters/{name}``              — update a filter file
-* ``POST /api/config/filters``                     — create a new filter file
+* ``PUT  /api/config/filters/{name}/raw``           — update a filter file (raw content)
+* ``POST /api/config/filters/raw``                 — create a new filter file (raw content)
 * ``GET  /api/config/filters/{name}/parsed``        — parse a filter file into a structured model
 * ``PUT  /api/config/filters/{name}/parsed``        — update a filter file from a structured model
 * ``GET  /api/config/actions``                     — list all action files
@@ -23,7 +23,8 @@ Endpoints:
 Note: ``GET /api/config/filters`` (enriched list) and
 ``GET /api/config/filters/{name}`` (full parsed detail) are handled by the
 config router (``config.py``), which is registered first and therefore takes
-precedence.  The raw-content variant is at ``/filters/{name}/raw``.
+precedence.  Raw-content read/write variants are at ``/filters/{name}/raw``
+and ``POST /filters/raw``.
 """
 
 from __future__ import annotations
@@ -347,9 +348,9 @@ async def get_filter_file_raw(
 
 
 @router.put(
-    "/filters/{name}",
+    "/filters/{name}/raw",
     status_code=status.HTTP_204_NO_CONTENT,
-    summary="Update a filter definition file",
+    summary="Update a filter definition file (raw content)",
 )
 async def write_filter_file(
     request: Request,
@@ -384,10 +385,10 @@ async def write_filter_file(
 
 
 @router.post(
-    "/filters",
+    "/filters/raw",
     status_code=status.HTTP_201_CREATED,
     response_model=ConfFileContent,
-    summary="Create a new filter definition file",
+    summary="Create a new filter definition file (raw content)",
 )
 async def create_filter_file(
     request: Request,