feat(nav): global ⌘K command palette

Adds a global command launcher reachable from anywhere via ⌘K (Mac) /
Ctrl+K (Win), or "/" when no input is focused.  Three sections:

- **Navigation** — every primary route from the top-bar nav, plus the
  full Admin sub-menu, role-gated against the session.
- **Recent activity** — last 5 audits and last 5 device observations,
  lazy-loaded once on first open from /api/dashboard/overview.
- **Companies** — fuzzy search against the active customer list from
  /api/companies, kicks in once the user types 2+ characters.
  Selecting a company deep-links to /configuration-items?company=<id>.

Top-bar exposes a small "Search · ⌘K" pill on md+ for discoverability,
sized to fit between the Status indicator and the Theme toggle.

Implementation:
- shadcn `command` primitive (uses cmdk under the hood); declined the
  bundled dialog overwrite to keep our existing dialog.tsx.
- CommandPalette mounted once in app/layout.tsx so it lives outside the
  AppNavigation re-renders.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -36,6 +36,7 @@
     "better-auth": "^1.4.10",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
+    "cmdk": "^1.1.1",
     "date-fns": "^4.1.0",
     "dotenv": "^17.2.3",
     "ioredis": "^5.9.0",