The music side's 'Clean Search History' automation now has a video counterpart so
it appears on the video Automations page too. Distinct action_type
video_clean_search_history (the system seeder keys on action_type, so reusing the
music key would collide), registered to the SAME shared handler so behaviour is
identical, scope='video' block (registry — users can build their own), and an
owned_by='video' system automation on the same 1h cadence. The music action/row
is untouched.
Seam tests: video-scoped only (not on music), music action still music-scoped,
exactly one video-owned system row at the 1h cadence, and it reuses the music
handler. Registration contract (EXPECTED_ACTION_NAMES) updated.
