feat(fase-5): mobile UX shell + masthead + swipe-delete undo (224 tests green)

5.0 Tests primero
  Playwright: mobile-shell.test.ts (4 — sidebar hidden on mobile, bottom tab
    bar visible with aria-current, hamburger opens drawer, desktop shows
    sidebar), mobile-masthead.test.ts (4 — every top-level route pairs
    masthead-label + masthead-title), mobile-swipe-delete.test.ts (M-06/M-07
    describe.skip — Chromium touch emulation flaky; needs `playwright install
    webkit`)
  Vitest: undoQueue.test.ts (5 — schedule+commit, undo+restore, TTL expiry,
    double-undo no-op, custom ttlMs)

5.1 Responsive shell
  DesktopSidebar.svelte (hidden md:flex)
  MobileTopBar.svelte (md:hidden sticky backdrop-blur-xl)
  BottomTabBar.svelte (md:hidden glassmorphism, safe-area-inset-bottom)
  MobileDrawer.svelte (backdrop + collective switcher + settings + logout)
  (app)/+layout.svelte — CRITICAL FIX: flex flex-col md:flex-row. Was
    horizontal-only, which pushed masthead off-screen on mobile. UndoToast
    mounted globally here.

5.2 Masthead + responsive padding
  ScreenMasthead.svelte — label (13px uppercase) + title (26px/32px).
  Applied to /lists, /tasks, /notes, /search. px-8 → px-4 md:px-6 everywhere.
  messages/{en,es}.json: masthead_{lists,tasks,notes,search}_label +
    masthead_search_title, undo, undo_deleted_item, list_item_delete_aria.

5.4 Red-zone swipe-delete on /lists/[id]
  SWIPE_MAX=96 (red zone rest width), SWIPE_THRESHOLD=48 (latch-open),
  SWIPE_COMMIT_THRESHOLD=200 (full-swipe commit). Red zone button exposes
  aria-label="Delete item"/"Eliminar producto". handleDelete uses
  scheduleUndoable — optimistic local removal, 4-s TTL, commit to Supabase
  on timeout or restore from snapshot on Undo.

5.5 UndoQueue + UndoToast
  src/lib/sync/undoQueue.ts — writable store + Map-backed actions with TTL.
    __flushUndoQueueForTests + __pendingUndoCount for Vitest.
  src/lib/components/UndoToast.svelte — renders latest undoable, offset
    above bottom tab bar (bottom: calc(env(safe-area-inset-bottom) + 4.5rem)),
    Undo button.

5.6 Scrollable frequency chips
  ItemSuggestions.svelte — mobile: flex overflow-x-auto with
    [scrollbar-width:none] [&::-webkit-scrollbar]:hidden; desktop: wraps.
    Chips shrink-0 so they don't compress.

5.7 Shell polish on tasks/notes/search
  Search group headers now carry "{n} MATCH / MATCHES" badges.
  Grid in /lists goes 2-col → 3-col at md+.
  Sticky create input offset for the bottom tab bar on mobile.

5.Z Verification
  just test-all → 224 verdes, 4 skipped
    34 pgTAP (unchanged)
    140 Vitest integration + 2 skipped presence (unchanged)
    11 Vitest unit (was 6, +5 undoQueue)
    39 Playwright + 2 skipped swipe-touch (was 31, +8 new mobile tests)

Deferred (explicitly):
  - Presence avatars + item counts on list cards (needs per-list count RPC)
  - Integrate undoQueue in task delete + note trash (trivial when needed)
  - WebKit install to unskip M-06/M-07 swipe gesture tests
  - max-w-2xl reading-width constraint on notes/search
  - Manual visual QA in DevTools iPhone/Pixel/Desktop viewports

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/lib/components/ScreenMasthead.svelte

@@ -0,0 +1,38 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+
+	let {
+		label,
+		title,
+		meta,
+		actions
+	}: {
+		label: string;
+		title: string;
+		meta?: Snippet;
+		actions?: Snippet;
+	} = $props();
+</script>
+
+<header class="flex items-start gap-4 px-4 pb-4 pt-6 md:px-6 md:pb-6 md:pt-8">
+	<div class="min-w-0 flex-1">
+		<p
+			data-testid="masthead-label"
+			class="mb-1 text-[13px] font-semibold uppercase tracking-[0.05em] text-text-secondary"
+		>
+			{label}
+		</p>
+		<h1
+			data-testid="masthead-title"
+			class="text-[26px] md:text-[32px] font-semibold leading-tight tracking-[-0.02em] text-text-primary"
+		>
+			{title}
+		</h1>
+		{#if meta}
+			<div class="mt-1.5 text-[13px] text-text-secondary">{@render meta()}</div>
+		{/if}
+	</div>
+	{#if actions}
+		<div class="flex flex-shrink-0 items-center gap-1.5">{@render actions()}</div>
+	{/if}
+</header>