feat(auth): add email verification UI flow

[PierreBrisorgueil]

Context

The Node stack is adding email verification on signup (see pierreb-devkit/Node#3216). The Vue stack needs the corresponding UI.

Backend reference

See pierreb-devkit/Node#3216 for the full backend spec:

• Signup creates account with emailVerified: false
• Verification email sent with JWT link
• GET /api/auth/verify/:token — verifies email
• POST /api/auth/verify/resend — resends verification email (rate-limited)
• OAuth users are auto-verified

Vue changes needed

1. Post-signup screen

After successful signup, redirect to a "Check your email" view instead of going straight to the app:

• Message: "We sent a verification link to {email}"
• "Resend email" button (calls POST /api/auth/verify/resend, rate-limited with cooldown timer)
• "Change email" link → back to signup

2. Verification landing page

New route: /auth/verify/:token

• On mount: calls GET /api/auth/verify/:token
• Success → "Email verified!" + auto-redirect to app (or login)
• Expired/invalid token → error message + "Resend verification email" button

3. Unverified user banner (optional)

If config.sign.requireEmailVerification is true and user is logged in but not verified:

• Show a persistent banner: "Please verify your email — Check your inbox or [resend]"
• Optionally restrict navigation to certain routes

4. Auth store updates

• Store emailVerified flag from user object
• Add actions: resendVerification(), verifyEmail(token)
• Update signup flow to handle the new intermediate state

Routes

{ path: '/auth/verify/:token', component: VerifyEmailView }
{ path: '/auth/verify/pending', component: VerifyEmailPendingView }

Config

The backend exposes /api/auth/config — should include requireEmailVerification flag so the frontend knows whether to enforce the flow or not.