Replace keyboard system with TanStack Hotkeys and jotai atoms

Remove react-hotkeys-hook, KeyboardProvider context, useRegisterShortcut
wrapper, and KeyboardHelpDialog component. Components now call TanStack
useHotkey/useHotkeySequence directly. Shared state uses jotai atoms in
lib/atoms/, shortcut metadata lives as a static const in lib/constants/.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -18,6 +18,7 @@
     "@base-ui/react": "^1.2.0",
     "@libsql/client": "^0.17.0",
     "@tabler/icons-react": "^3.37.1",
+    "@tanstack/react-hotkeys": "^0.3.1",
     "better-auth": "^1.5.0",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
@@ -25,13 +26,13 @@
     "date-fns": "^4.1.0",
     "drizzle-orm": "1.0.0-beta.15-859cf75",
     "embla-carousel-react": "^8.6.0",
+    "jotai": "^2.18.0",
     "motion": "^12.34.3",
     "next": "16.1.6",
     "node-vibrant": "^4.0.4",
     "react": "19.2.4",
     "react-day-picker": "^9.14.0",
     "react-dom": "19.2.4",
-    "react-hotkeys-hook": "^5.2.4",
     "react-resizable-panels": "^4.7.0",
     "recharts": "2.15.4",
     "shadcn": "^3.8.5",