feat(ui): full frontend redesign to the Sentry-style design system

Replace the legacy UI with the dark, mono-accent design language from
design/23-sentry.html across every non-canvas surface.

- PlatformShell: fixed 252px sidebar with grouped nav (Platform /
  Operate / Workspace), brand mark, user card, and a topbar with
  search (Cmd+K palette), env badge, upgrade, notifications, and
  theme toggle; mobile collapses to a top bar with horizontal nav
- New shared component kit in shared/components/sentry.tsx:
  SPageHead, SStat, SCard, STable, SSection, SPill, Ticks, Seg,
  GhostBtn/QuietBtn/IconBtn, status tone helpers
- New DashboardPage at / — stats row, per-node CPU chart with
  1h/24h/7d ranges, resource usage tick strips, anomaly box,
  node summary table, recent deployments and project cards;
  real API data with demo-mode fixtures
- Landing page moved to /landing and rebuilt: live host telemetry
  window, install strip, feature grid, template catalog, docs
- Every page (Projects, Templates, Builds, Databases, HA,
  Operations, Activity, Security, Usage, Docs, People, Settings,
  Audit Logs, Webhooks, Admin, NodeDetail, ServiceDetail, auth,
  setup, not-found) migrated to the new kit and tokens
- Nav active state resolves by longest matching href
- Canvas internals intentionally untouched — separate pass

Verified: tsc --noEmit, eslint, vite build, Playwright walkthrough
of every route at desktop and mobile widths (demo + live session).

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/frontend/src/shared/components/CommandPalette.tsx

@@ -134,6 +134,17 @@ function CommandPaletteContent({
         onClose();
       },
     },
+    {
+      id: 'goto-dashboard',
+      label: 'Go to Dashboard',
+      icon: LayoutGrid,
+      shortcut: 'H',
+      category: 'Navigate',
+      action: () => {
+        onNavigate?.('dashboard');
+        onClose();
+      },
+    },
     {
       id: 'goto-canvas',
       label: 'Go to Canvas',
@@ -205,7 +216,7 @@ function CommandPaletteContent({
       />
       <div className="absolute left-1/2 top-[20%] -translate-x-1/2 w-full max-w-xl">
         <Command
-          className="panel overflow-hidden"
+          className="s-card !p-0 overflow-hidden shadow-2xl shadow-black/50"
           loop
         >
           <div className="flex items-center gap-3 px-4 py-3 border-b border-[var(--border-subtle)]">
@@ -228,7 +239,7 @@ function CommandPaletteContent({
 
             {Object.entries(groupedCommands).map(([category, items]) => (
               <Command.Group key={category} heading={category} className="mb-2">
-                <div className="px-2 py-1.5 text-[10px] font-semibold uppercase tracking-widest text-[var(--text-muted)]">
+                <div className="px-2 py-1.5 v-mono text-[10px] uppercase tracking-[0.14em] text-[var(--text-muted)]">
                   {category}
                 </div>
                 {items.map((item) => {
@@ -238,9 +249,9 @@ function CommandPaletteContent({
                       key={item.id}
                       value={item.label}
                       onSelect={item.action}
-                      className="flex items-center gap-3 px-3 py-2.5 rounded-[var(--radius-md)] cursor-pointer text-[var(--text-secondary)] hover:bg-[var(--surface-muted)] hover:text-[var(--text-primary)] aria-selected:bg-[var(--accent-primary-soft)] aria-selected:text-[var(--accent-primary)] transition-colors"
+                      className="flex items-center gap-3 px-3 py-2 rounded-[var(--radius-md)] cursor-pointer text-[var(--text-secondary)] hover:bg-[var(--surface-muted)] hover:text-[var(--text-primary)] aria-selected:bg-[var(--accent-primary-soft)] aria-selected:text-[var(--accent-primary)] transition-colors"
                     >
-                      <Icon size={18} className="text-[var(--text-muted)]" />
+                      <span className="s-ibox !h-7 !w-7"><Icon /></span>
                       <div className="flex-1">
                         <div className="text-sm font-medium">{item.label}</div>
                         {item.description && (