Add filter discovery endpoints with active/inactive status (Task 2.1)

- Add list_filters() and get_filter() to config_file_service.py:
  scans filter.d/, parses [Definition] + [Init] sections, merges .local
  overrides, and cross-references running jails to set active/used_by_jails
- Add FilterConfig.active, used_by_jails, source_file, has_local_override
  fields to the Pydantic model; add FilterListResponse and FilterNotFoundError
- Add GET /api/config/filters and GET /api/config/filters/{name} to config.py
- Remove the shadowed GET /api/config/filters list route from file_config.py;
  rename GET /api/config/filters/{name} raw variant to /filters/{name}/raw
- Update frontend: fetchFilterFiles() adapts FilterListResponse -> ConfFilesResponse;
  add fetchFilters() and fetchFilter() to api/config.ts; remove unused
  fetchFilterFiles/fetchActionFiles calls from useConfigActiveStatus
- Fix ConfigPageLogPath test mock to include fetchInactiveJails and related
  exports introduced by Stage 1
- Backend: 169 tests pass, mypy --strict clean, ruff clean
- Frontend: 63 tests pass, tsc --noEmit clean, eslint clean

frontend/src/hooks/useConfigActiveStatus.ts

@@ -12,11 +12,7 @@
 
 import { useCallback, useEffect, useRef, useState } from "react";
 import { fetchJails } from "../api/jails";
-import {
-  fetchActionFiles,
-  fetchFilterFiles,
-  fetchJailConfigs,
-} from "../api/config";
+import { fetchJailConfigs } from "../api/config";
 import type { JailConfig } from "../types/config";
 import type { JailSummary } from "../types/jail";
 
@@ -44,8 +40,10 @@ export interface UseConfigActiveStatusResult {
 // ---------------------------------------------------------------------------
 
 /**
- * Fetch jails, jail configs, filter files, and action files in parallel and
- * derive active-status sets for each config type.
+ * Fetch jails and jail configs, then derive active-status sets for each
+ * config type.  Active status is computed from live jail data; filter and
+ * action files are not fetched directly because their active state is already
+ * available via {@link fetchFilters} / {@link fetchActions}.
  *
  * @returns Active-status sets, loading flag, error, and refresh function.
  */
@@ -69,10 +67,8 @@ export function useConfigActiveStatus(): UseConfigActiveStatusResult {
     Promise.all([
       fetchJails(),
       fetchJailConfigs(),
-      fetchFilterFiles(),
-      fetchActionFiles(),
     ])
-      .then(([jailsResp, configsResp, _filterResp, _actionResp]) => {
+      .then(([jailsResp, configsResp]) => {
         if (ctrl.signal.aborted) return;
 
         const summaries: JailSummary[] = jailsResp.jails;