✨(summary) add optional satisfaction survey footer

Add a footer to transcription outputs linking to an external satisfaction
survey. The survey URL is built from TRANSCRIPTION_SATISFACTION_FORM_BASE_URL.
When TRANSCRIPTION_SATISFACTION_FORM_BASE_URL is unset or None, the
footer is omitted.

src/summary/tests/api/test_api_tasks.py

@@ -27,6 +27,7 @@ class TestTasks:
                 "owner_timezone": "UTC",
                 "language": None,
                 "download_link": "https://example.com/file.mp4",
+                "form_link": "https://satisfaction.com?room_id=test",
             },
         )