test(front): add live integration test suite

[TheRealAgentK]

Background

Front was migrated to SDK 2.0.0 in #288 with 77 new unit tests, but no tests/test_front_integration.py was added.

Front uses platform OAuth, so e2e coverage requires a manually obtained access token.

Acceptance criteria

• front/tests/test_front_integration.py following the writing-integration-tests skill
• Read-only smoke coverage across the major endpoints (conversations, messages, channels, contacts)
• Specifically cover the multipart-upload helpers in send_message and send_channel_message (lines 404 and 689) — those return raw {"error": ...} dicts that aren't exercised by mocked unit tests
• Destructive tests (send_message, send_channel_message, create_conversation) gated with @pytest.mark.destructive
• Token-extraction recipe documented at the top of the test file
• pytest front/ -m integration passes locally

Related

• fix(front): upgrade to SDK 2.0.0, add unit tests #288 (SDK 2.0.0 upgrade)