Feature Policies API + Invitations Policies (#375)

- Added Feature Policy API: a declarative system to enable/disable/modify default behavior in the SaaS kit
- Team invitation policies with pre-checks using the Feature Policy API: Invite Members dialog now shows loading, errors, and clear reasons when invitations are blocked
- Version bump to 2.16.0 and widespread dependency updates (Supabase, React types, react-i18next, etc.).
- Added comprehensive docs for the new policy system and orchestrators.
- Subscription cancellations now trigger immediate invoicing explicitly

apps/e2e/tests/team-accounts/team-invitation-mfa.spec.ts

@@ -13,7 +13,7 @@ test.describe('Team Invitation with MFA Flow', () => {
     const invitations = new InvitationsPageObject(page);
 
     await auth.loginAsUser({
-      email: 'test@makerkit.dev',
+      email: 'owner@makerkit.dev',
     });
 
     const teamName = `test-team-${Math.random().toString(36).substring(2, 15)}`;