Per-project task list + purge/cancel actions

[Eyalm321]

Type: AFK

What to build

From a project's task lane, let the user drill into the actual tasks (id / title / state / attempts) and act on them: purge terminal tasks (done/failed/dead) and cancel an in-flight task. Wired to the control API.

Acceptance criteria

• Clicking a lane shows that lane's tasks (id, title, state, attempts)
• A "purge terminal" action removes done/failed/dead tasks for the queue and the UI updates
• A per-task cancel action fails/removes an in-flight task
• Actions report success/failure and never wedge the UI

Blocked by

• Per-project task state lanes in the sidebar #7