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/functions/backend/db/tasks/assign-ownerless-tasks.ts

@@ -0,0 +1,10 @@
+import passOnBotTasks from "./pass-on-bot-tasks";
+
+/**
+ * At boot: every task belongs to a bot. Workspace tasks left without one
+ * by earlier versions ("shared") go to the workspace's admin bot, else the
+ * coordinator.
+ */
+export default async function assignOwnerlessTasks() {
+    return await passOnBotTasks({});
+}