Scope workspace tasks to the bot that has them

A workspace's task now carries the bot that has it there (bot_id with
workspace_id), or none while it's shared. A bot reaches its own list and,
in its workspaces, its own tasks plus the shared ones; a workspace admin
every task there. Bots create workspace tasks for themselves by default,
take a shared one by starting it, and hand-overs record the new bot.
Removing or deleting a bot makes its workspace tasks shared again. The
conversation's Tasks modal shows that bot's tasks in the workspace.

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

src/functions/backend/db/tasks/purge-task-media.ts

@@ -3,7 +3,7 @@ import type { BUN_SQLITE_COBBLE_TASK_MEDIA } from "@/db/types/db";
 
 type Params = {
     /**
-     * A bot's own tasks, or a workspace's.
+     * A bot's own list (not what it has in workspaces), or a workspace's.
      */
     bot_id?: number | string | null;
     workspace_id?: number | string | null;
@@ -25,7 +25,7 @@ export async function grabTaskMediaIds({ bot_id, workspace_id }: Params): Promis
         await BunSQLite.sql<BUN_SQLITE_COBBLE_TASK_MEDIA>({
             sql: `SELECT tm.media_id FROM task_media tm
                 JOIN tasks t ON t.id = tm.task_id
-                WHERE t.${column} = ? AND tm.bot_file_id IS NULL`,
+                WHERE t.${column} = ? ${workspace_id ? "" : "AND t.workspace_id IS NULL"} AND tm.bot_file_id IS NULL`,
             values: [Number(owner)],
         })
     ).payload || [];