feat(ui): replace Switch with TogglePill per design audit (#687)

* chore: ignore local design-system references

Adds frontend/DESIGN.md and .design-bundle/ to .gitignore so the
design-system reference and the audit handoff bundle stay local
to each contributor's machine.

* feat(ui): replace Switch with TogglePill per design audit

Adds a mono-uppercase ON/OFF pill that replaces the sliding Switch
across every call site. The pill uses role="switch" plus aria-checked,
tints success-green when on and neutral card-tone when off, and holds
a stable 60px min-width so the label flip does not shift layout. It
reinforces the tracked-mono uppercase pattern already used for kicker
labels and table column headers, and echoes the UP/DN status language
of the sidebar stack list.

- Add TogglePill component (frontend/src/components/ui/toggle-pill.tsx)
- Replace 17 Switch call sites across 10 files (settings sections,
  SSO providers, scheduled operations, network topology, resources,
  stack auto-heal)
- Remove unused Switch wrapper and radix primitive
- Drop the @radix-ui/react-switch dependency

frontend/src/components/settings/AccountSection.tsx

@@ -3,7 +3,7 @@ import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { Label } from '@/components/ui/label';
 import { Badge } from '@/components/ui/badge';
-import { Switch } from '@/components/ui/switch';
+import { TogglePill } from '@/components/ui/toggle-pill';
 import { Separator } from '@/components/ui/separator';
 import { AlertTriangle, RefreshCw, Shield, ShieldCheck } from 'lucide-react';
 import { MfaEnrollDialog } from '@/components/mfa/MfaEnrollDialog';
@@ -179,9 +179,9 @@ export function AccountSection({ authData, onAuthDataChange, onPasswordChange, i
                                                 SSO logins skip the second factor by default.
                                             </div>
                                         </div>
-                                        <Switch
+                                        <TogglePill
                                             checked={mfa.sso_enforce_mfa}
-                                            onCheckedChange={handleBypassToggle}
+                                            onChange={handleBypassToggle}
                                             disabled={togglingBypass}
                                         />
                                     </div>