fix(tasks): producer diagnostics name the seam, not one implementation

Review feedback (tianyicui, PR #657 inline): the missing-service message
should mention dsh-tasks, which defines ctx.tasks, rather than promoting a
specific backend. The seam's own surfaces (README, the direct-mount fence)
keep pointing at implementations, so the pointer chain still lands on
dsh-tasks-local without the producer strings going stale when another
backend becomes the recommended default. Agent Note updated accordingly
(en+zh, re-recorded).

packages/bash/tool-bash/src/index.ts

@@ -533,7 +533,7 @@ export function apply(ctx: Context, config: Config = {}): void {
         }
         const tasks = ctx.get('tasks')
         if (tasks === undefined) {
-          throw new Error('background tasks unavailable: load @deepseek-ai/dsh-tasks-local and @deepseek-ai/dsh-tool-tasks')
+          throw new Error('background tasks unavailable: load @deepseek-ai/dsh-tasks and @deepseek-ai/dsh-tool-tasks')
         }
         // The caller owns cancellation until ctx.tasks commits detached ownership.
         if (exec.signal.aborted) {