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/tests/tools.spec.ts

@@ -475,7 +475,7 @@ describe('background execution through the task runtime', () => {
     const ctx = await setup() // no LocalTaskService / ToolTasks
     const result = await call(ctx, 'bash', { command: 'sleep 60', description: 'test command', run_in_background: true })
     expect(result.isError).toBe(true)
-    expect(text(result)).toContain('background tasks unavailable: load @deepseek-ai/dsh-tasks-local and @deepseek-ai/dsh-tool-tasks')
+    expect(text(result)).toContain('background tasks unavailable: load @deepseek-ai/dsh-tasks and @deepseek-ai/dsh-tool-tasks')
   })
 
   it('a pre-aborted call is skipped before the process starts', async () => {