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/styles/login.css

@@ -55,3 +55,11 @@
   font-size: var(--text-sm);
   margin-bottom: var(--space-4);
 }
+
+.login-version {
+  margin-top: var(--space-4);
+  font-size: var(--text-xs);
+  color: var(--color-text-tertiary, var(--color-text-secondary));
+  text-align: center;
+  opacity: 0.6;
+}