WebAuthn biometric + PWA widget + UI header fixes + mobile responsive

- WebAuthn: register/auth options, device management
- PWA widget page + manifest shortcuts
- Group schedule endpoint (timezones + locations)
- UI #3-#6: compact headers on tasks/calendar/projects/goals
- UI #9: mobile responsive top bars
- webauthn_credentials table

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/src/features/registry.js

@@ -8,6 +8,7 @@ const features = [
     { name: "kanban", path: "./kanban", prefix: "/api/v1" },
     { name: "ai-briefing", path: "./ai-briefing", prefix: "/api/v1" },
     { name: "webhooks-outgoing", path: "./webhooks-outgoing", prefix: "/api/v1" },
+    { name: "webauthn", path: "./webauthn", prefix: "/api/v1" },
 ];
 
 async function registerFeatures(app) {