feat: add team invitation acceptance flow with email link routing

Implement end-to-end invitation acceptance: neutral entry route validates
token and routes to register (new users), login (existing users), or
auto-accepts (authenticated users). Handles 2FA token survival via
session, email case-insensitive matching, and dedicated error pages.

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

app/Mail/TeamInvitationMail.php

@@ -48,7 +48,7 @@ class TeamInvitationMail extends Mailable implements ShouldQueue
             with: [
                 'workspaceName' => $this->workspace->name,
                 'roleLabel' => $roleLabels[$this->invitation->role] ?? $this->invitation->role,
-                'registerUrl' => route('register', ['invitation' => $this->invitation->token]),
+                'acceptUrl' => route('team.invitation.accept', $this->invitation->token),
                 'expiresAt' => $this->invitation->expires_at->format('d/m/Y à H:i'),
             ]
         );