system-monitor: /system-monitor route (CPU/mem/disk/processes) + page titles

- Backend GET /api/system-monitor/stats: one snapshot — CPU overall + per-core
  (two /proc/stat samples), memory + swap (/proc/meminfo), disks (df), load,
  uptime, top-20 processes (ps). Owner-only via the account gate.
- Frontend /system-monitor screen: polls every 2s; CPU/Memory/Disks cards with
  bars + per-core mini-bars, top-processes table. Nav dock "Monitor" item.
- Register /music and /system-monitor in usePageTitle RULES so the browser tab
  and editable header title update on those routes (/music was missing too).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/apps/officer-web/state/usePageTitle.ts

@@ -15,6 +15,8 @@ const RULES: TitleRule[] = [
   { match: (p) => p.startsWith('/chat'), title: 'Chat' },
   { match: (p) => p.startsWith('/email'), title: 'Email' },
   { match: (p) => p.startsWith('/files'), title: 'Files' },
+  { match: (p) => p.startsWith('/music'), title: 'Music' },
+  { match: (p) => p.startsWith('/system-monitor'), title: 'System Monitor' },
   { match: (p) => p.startsWith('/code-editor'), title: 'Code Editor' },
   { match: (p) => p.startsWith('/projects'), title: 'Projects' },
   { match: (p) => p.startsWith('/task-logs'), title: 'Task Logs' },