file manager: implement the tree filter (categories + per-service)

Fill in the scaffolded file-tree filter:

- FS_FILTER_GROUPS: Identifiers, PLMN selection, Provider names,
  WLAN/I-WLAN, SMS-related and CB-related (cell broadcast), each with
  its exact file list; plus one option per file-backed feature of
  SERVICES_FS_MAP (svc:<feature>).
- "All" is the default and exclusive; a top-level "Custom files"
  option matches the injected custom-file nodes by their flag.
- fsFilterIndexBuild inverts name -> criterion set; pysimFsFilterMatch
  matches by name (and custom by flag); pysimFsFilterShow keeps a
  directory while it has a matching (loaded) descendant, and keeps
  never-expanded directories.  The dropdown renders All / Custom files
  and three optgroups (Identifiers / PLMN / Services).
- i18n EN/RU for the new labels.

Frontend 1145 tests green (fs_filter.test.js 19).

frontend/tests/fs_render.test.js

@@ -26,6 +26,7 @@ code += 'var pysimFsFilter = new Set();\n';
 code += extractFunc(html, 'pysimFsSortChildren') + '\n';
 code += extractFunc(html, 'pysimFsNodePath') + '\n';
 code += extractFunc(html, 'pysimFsFilterMatch') + '\n';
+code += extractFunc(html, 'pysimFsFilterShow') + '\n';
 code += extractFunc(html, 'pysimFsRenderNode') + '\n';
 code += 'globalThis.esc = s => s;\nglobalThis.t = s => s;\n';
 eval(code);