feat(frontend): merge top-bar search with the filter bar, expose kind/created filters

Unify the upstream top-bar search box and the local SearchFilterBar into
one filtering capability sharing a single state store, with the URL as
its projection:

- lib/stores/filter.svelte.ts: module-level $state store, the single
  source of truth; every surface mutates the same proxy in place
- lib/composables/useFilterUrlSync.svelte.ts: one $effect serves both
  directions (URL -> store adoption, store -> URL replaceState write)
  with echo suppression so the loop settles in one round-trip
- FilterFields.svelte: the five selects (type/size/modified/created/
  kind) + recursive switch; word lists and i18n labels live in one
  place; SearchFilterBar reuses it instead of its own copies
- TopBarFilterPanel.svelte: dropdown panel anchored inside the top-bar
  search input (in-field toggle button with active-count badge);
  Escape/outside-click close, no overlay stacking with suggestions
- FilterChips.svelte: dismissible chips on /search, which is now
  URL-driven and loses its three inline <select>s
- New dimensions the backend already supported: kind (file/folder,
  resource_types) and created (created_after); URL keys q/type/size/
  date/created/kind/recursive, non-defaults only, unknown values
  degrade to defaults
- /files keeps in-place filtering (no navigation); folderTarget
  carries filter params through folder entry; ?file= and in/scope
  survive filter writes
- topbar.css: input right padding reserves the three in-field controls

Backend unchanged.

Co-Authored-By: Claude Code <noreply@anthropic.com>

frontend/static/locales/pl.json

@@ -422,7 +422,15 @@
     "advanced": "Filtry",
     "recursive": "Uwzględnij podfoldery",
     "results_count": "Wyniki: {{n}}",
-    "clear_keyword": "Wyczyść wyszukiwanie"
+    "clear_keyword": "Wyczyść wyszukiwanie",
+    "modified_label": "Modified",
+    "created_label": "Created",
+    "kind_label": "Items",
+    "kind": {
+      "all": "Files and folders",
+      "file": "Files only",
+      "folder": "Folders only"
+    }
   },
   "files": {
     "name": "Nazwa",