Phase 10: command palette, settings, backup/restore, sample campaign

- Command palette (Ctrl/Cmd+K): fuzzy search over pages + active-campaign
  characters/notes/NPCs/quests + actions; keyboard nav; header ⌘K button
- Settings page: theme, full backup export/import (restore replaces all in one
  transaction), load sample campaign, danger-zone clear-all
- Backup lib (src/lib/io/backup.ts) snapshots every table; sample seeder
  (src/lib/sample.ts) builds a demo campaign
- Header gets ⌘K + settings gear; routes + nav wired

Backup round-trip unit tests + command-palette/settings e2e.
(Deferred from this phase, noted in plan: audio, Discord/Foundry/Roll20, i18n,
push notifications.)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app/RootLayout.tsx

@@ -1,5 +1,7 @@
+import { useEffect, useState } from 'react';
 import { Link, Outlet, useRouterState } from '@tanstack/react-router';
 import { useUiStore } from '@/stores/uiStore';
+import { CommandPalette } from '@/components/CommandPalette';
 import { useActiveCampaign, useCampaigns } from '@/features/campaigns/hooks';
 import { cn } from '@/lib/cn';
 import { ErrorBoundary } from '@/components/ui/ErrorBoundary';
@@ -53,6 +55,19 @@ function ThemeToggle() {
 
 export function RootLayout() {
   const pathname = useRouterState({ select: (s) => s.location.pathname });
+  const [paletteOpen, setPaletteOpen] = useState(false);
+
+  // Global Ctrl/Cmd+K opens the command palette.
+  useEffect(() => {
+    const onKey = (e: KeyboardEvent) => {
+      if ((e.metaKey || e.ctrlKey) && e.key.toLowerCase() === 'k') {
+        e.preventDefault();
+        setPaletteOpen((v) => !v);
+      }
+    };
+    window.addEventListener('keydown', onKey);
+    return () => window.removeEventListener('keydown', onKey);
+  }, []);
 
   return (
     <div className="flex h-full flex-col">
@@ -78,6 +93,10 @@ export function RootLayout() {
           })}
         </nav>
         <div className="ml-auto flex items-center gap-2">
+          <Button size="sm" variant="ghost" onClick={() => setPaletteOpen(true)} title="Command palette (Ctrl/Cmd+K)" aria-label="Open command palette">
+            ⌘K
+          </Button>
+          <Link to="/settings" className="rounded-md p-1.5 text-sm text-muted hover:text-ink" title="Settings" aria-label="Settings">⚙</Link>
           <CampaignSwitcher />
           <ThemeToggle />
         </div>
@@ -90,6 +109,7 @@ export function RootLayout() {
       </main>
 
       <RollTray />
+      {paletteOpen && <CommandPalette onClose={() => setPaletteOpen(false)} />}
     </div>
   );
 }