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/src/lib/components/AppShell.test.ts

@@ -88,3 +88,49 @@ it('submits a search and routes to /search', async () => {
 	await fireEvent.click(screen.getByTestId('appshell-search-submit-btn'));
 	await waitFor(() => expect(goto).toHaveBeenCalledWith('/search?q=report'));
 });
+
+it('opens the filter panel, and its presets ride along on submit', async () => {
+	render(AppShell, { props: { children } });
+	// Panel opens from the toggle inside the search input…
+	await fireEvent.click(screen.getByTestId('appshell-filter-toggle-btn'));
+	expect(screen.getByTestId('appshell-filter-panel')).toBeTruthy();
+	// …and picking a preset lights the toggle's badge (shared store).
+	await fireEvent.change(screen.getByTestId('filter-type-select'), {
+		target: { value: 'image' }
+	});
+	expect(screen.getByTestId('appshell-filter-toggle-btn').textContent).toContain('1');
+	// Submitting carries the preset into the search URL.
+	const input = screen.getByTestId('appshell-search-input');
+	await fireEvent.input(input, { target: { value: 'report' } });
+	await fireEvent.click(screen.getByTestId('appshell-search-submit-btn'));
+	await waitFor(() => expect(goto).toHaveBeenCalledWith('/search?q=report&type=image'));
+	// Submit closes the panel; reopen it and "Clear filters" resets the
+	// presets — the badge drops and the next submit is param-free.
+	await fireEvent.click(screen.getByTestId('appshell-filter-toggle-btn'));
+	await fireEvent.click(screen.getByTestId('appshell-filter-clear-btn'));
+	expect(screen.getByTestId('appshell-filter-toggle-btn').textContent!.includes('1')).toBe(false);
+	await fireEvent.input(input, { target: { value: 'again' } });
+	await fireEvent.click(screen.getByTestId('appshell-search-submit-btn'));
+	await waitFor(() => expect(goto).toHaveBeenCalledWith('/search?q=again'));
+	// Leave the shared store clean for the other tests in this file.
+	await fireEvent.click(screen.getByTestId('appshell-filter-toggle-btn'));
+	await fireEvent.click(screen.getByTestId('appshell-filter-clear-btn'));
+});
+
+it('closes the filter panel on Escape and on outside click', async () => {
+	render(AppShell, { props: { children } });
+	await fireEvent.click(screen.getByTestId('appshell-filter-toggle-btn'));
+	expect(screen.getByTestId('appshell-filter-panel')).toBeTruthy();
+	await fireEvent.click(screen.getByTestId('appshell-filter-done-btn'));
+	expect(screen.queryByTestId('appshell-filter-panel')).toBeNull();
+	// Outside click (window-level handler) reopens-then-closes too.
+	await fireEvent.click(screen.getByTestId('appshell-filter-toggle-btn'));
+	expect(screen.getByTestId('appshell-filter-panel')).toBeTruthy();
+	await fireEvent.click(screen.getByTestId('shell-child'));
+	expect(screen.queryByTestId('appshell-filter-panel')).toBeNull();
+	// Escape closes it as well.
+	await fireEvent.click(screen.getByTestId('appshell-filter-toggle-btn'));
+	expect(screen.getByTestId('appshell-filter-panel')).toBeTruthy();
+	await fireEvent.keyDown(window, { key: 'Escape' });
+	expect(screen.queryByTestId('appshell-filter-panel')).toBeNull();
+});