Mirror the row-level delete affordance the loops sidebar already
has. Loops was wired earlier; research had a bare title-only card
with no way to remove a stale topic.
- cm-db: research_topics::delete cascades via existing FK rules
(research_topic_agents, research_publish_approvals, and the new
research_outcomes all CASCADE on topic_id; topology_runs's
research_topic_id back-ref is SET NULL so historical runs stay).
- cm-api: DELETE /api/research/{id} → 204. Idempotent.
- Frontend: deleteTopic helper. ResearchList row is now a card
with the existing title/status/outcome header plus a trash icon
that flips the card into an inline "Delete topic + all outcomes?"
confirm strip. Confirm → red Delete / gray Cancel. If the
deleted topic was selected, selection clears; local counter
bumps the list refetch without waiting on a parent.
