feat(cloud): complete secure invitation experience

tests/unit_tests/workspace/test_invitation_delivery.py

@@ -86,3 +86,20 @@ async def test_environment_mapping_enables_provider_without_leaking_secret(monke
         'https://env.langbot.example/invitations/accept#token=lbi_secret'
     )
     assert service.capability() == {'enabled': True, 'provider': 'smtp'}
+
+
+async def test_cloud_invitation_email_has_branded_html_plain_fallback_and_expiry_copy():
+    service = InvitationDeliveryService(_app({}))
+    link = 'https://cloud.langbot.app/invitations/accept#token=lbi_secret&next=<unsafe>'
+
+    text = service._plain_text('Research & Development', link)
+    html = service._html('Research & Development', link)
+
+    assert 'LangBot Cloud' in text
+    assert 'Research & Development' in text
+    assert '7 days' in text
+    assert link in text
+    assert 'Accept invitation' in html
+    assert 'Research &amp; Development' in html
+    assert 'expires in 7 days' in html
+    assert 'lbi_secret&amp;next=&lt;unsafe&gt;' in html