fix(auth): resolve post-login navigate race condition and add version display (#68) (#70)

Root cause: when auth.me() failed during initial navigation, the catch block
called navigate('/login') without clearing _pendingLoginRedirect. The outer
finally then fired a second concurrent navigate('/login'), which held
isNavigating=true while running. If the user submitted the login form (or
iCloud Keychain autofilled credentials) before the second navigation
completed, navigate('/', user) was silently blocked by the isNavigating guard —
login appeared to succeed but the app never advanced to the dashboard.

Fix: clear _pendingLoginRedirect in the catch block so the finally handler
does not spawn the duplicate navigation.

Also adds a GET /api/v1/version endpoint (no auth required) and shows the
version on the login page, so users can verify their PWA has received the
latest cached JS.

Resolves #68

Co-authored-by: Ulas Kalayci <ulas.kalayci@googlemail.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

public/locales/de.json

@@ -618,7 +618,8 @@
     "loginButton": "Anmelden",
     "loggingIn": "Wird angemeldet …",
     "tooManyAttempts": "Zu viele Versuche. Bitte warte kurz.",
-    "invalidCredentials": "Ungültige Anmeldedaten."
+    "invalidCredentials": "Ungültige Anmeldedaten.",
+    "version": "v{{version}}"
   },
   "install": {
     "title": "Oikos installieren",
@@ -676,4 +677,4 @@
     "pendingBadgeTitle": "{{count}} fällige Erinnerung",
     "pendingBadgeTitlePlural": "{{count}} fällige Erinnerungen"
   }
-}
+}