Give every task a bot: drop shared workspace tasks

A workspace task with no bot was seen by every bot working there. Now a
task can't be saved without a bot, a worker reaches only its own (the
workspace admin and the coordinator still reach all), the workspace page
picks who has a new task, and a bot leaving a workspace or deleted passes
its tasks there to the workspace's admin bot, else the coordinator (also
at boot for rows without a bot).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/components/general/task-detail-panel.tsx

@@ -231,7 +231,7 @@ export default function TaskDetailPanel({ task, can_manage, onChanged, onDeleted
                             <Span className="min-w-0 truncate">{task.bot_name || `Bot ${task.bot_id}`}</Span>
                         </>
                     ) : (
-                        <Span className="text-ink-secondary">Shared, nobody has taken it up yet</Span>
+                        <Span className="text-ink-secondary">No bot</Span>
                     )}
                 </TaskFactRow>
                 <TaskFactRow label="Where">