Passkey browser compatibility: detect support, magic link fallback

- Login: hide passkey button when browser lacks WebAuthn, default to
  magic link mode, hide "back to passkey" link
- Register: detect passkey support and offer magic link registration as
  fallback. New server-side registerWithMagicLink() creates account
  without credential and sends verification email.
- Home: show passkey count for logged-in users, show amber unsupported
  message instead of hiding the add-passkey prompt entirely
- i18n: add passkeyNotSupported, passkeyNotSupportedRegister,
  registerWithMagicLink, passkeyStatus keys (en + de)

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

packages/i18n/src/locales/de.ts

@@ -106,6 +106,8 @@ export default {
     addPasskey: "Passkey hinzufügen",
     settingUp: "Wird eingerichtet...",
     passkeyAdded: "Passkey hinzugefügt! Du kannst dich jetzt sofort auf diesem Gerät anmelden.",
+    passkeyStatus: "{{count}} Passkey registriert",
+    passkeyStatus_other: "{{count}} Passkeys registriert",
     routes: {
       title: "Routen",
       myRoutes: "Meine Routen",
@@ -147,6 +149,9 @@ export default {
       registerDescription: "Registriere dich mit einem Passkey — kein Passwort nötig.",
       registerWithPasskey: "Mit Passkey registrieren",
       creatingPasskey: "Erstelle Passkey...",
+      passkeyNotSupported: "Dein Browser unterstützt keine Passkeys. Bitte verwende einen anderen Browser zur Registrierung.",
+      passkeyNotSupportedRegister: "Dein Browser unterstützt keine Passkeys. Du kannst dich stattdessen per Magic Link registrieren und später einen Passkey hinzufügen.",
+      registerWithMagicLink: "Per Magic Link registrieren",
     },
   },
 } as const;

packages/i18n/src/locales/en.ts

@@ -106,6 +106,8 @@ export default {
     addPasskey: "Add Passkey",
     settingUp: "Setting up...",
     passkeyAdded: "Passkey added! You can now sign in instantly on this device.",
+    passkeyStatus: "{{count}} passkey registered",
+    passkeyStatus_other: "{{count}} passkeys registered",
     routes: {
       title: "Routes",
       myRoutes: "My Routes",
@@ -147,6 +149,9 @@ export default {
       registerDescription: "Register with a passkey — no password needed.",
       registerWithPasskey: "Register with Passkey",
       creatingPasskey: "Creating passkey...",
+      passkeyNotSupported: "Your browser does not support passkeys. Please use a different browser to register.",
+      passkeyNotSupportedRegister: "Your browser doesn't support passkeys. You can register with a magic link instead and add a passkey later from a supported browser.",
+      registerWithMagicLink: "Register with Magic Link",
     },
   },
 } as const;