fix(harness): add global progress to subagent completion notifications

[guslegend0510]

Summary

• Add session-scoped task progress to background subagent completion notifications, for example: [3/8 tasks terminal]
• Count COMPLETED, FAILED, and CANCELLED tasks as terminal
• Share the same MessageBus wiring logic between static and dynamic subagent middleware
• Preserve the original notification and wakeup behavior when task progress cannot be queried
• Remove the duplicated MessageBus wiring implementation from HarnessAgent.Builder

Behavior

Completion notifications now include a best-effort snapshot of the current session's task progress:

Background subagent task 'task-3' (agent=worker) has completed [3/8 tasks terminal].

Tasks from other sessions are not included.
If TaskRepository.listTasks(...) fails, the notification falls back to the original format and is still delivered to the inbox with a wakeup signal.
Testing
Added tests for [1/5 tasks terminal] and [5/5 tasks terminal]
Verified COMPLETED, FAILED, and CANCELLED are terminal, while RUNNING is not
Verified session isolation
Verified fallback behavior when task progress lookup fails
Verified static and dynamic middleware use the same notification format
Spotless passed
agentscope-core: 2294 tests passed
agentscope-harness: 838 tests passed
Closes #2792

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../harness/agent/middleware/SubagentsMiddleware.java	80.00%	1 Missing and 2 partials ⚠️
...s/agent/middleware/DynamicSubagentsMiddleware.java	66.66%	0 Missing and 1 partial ⚠️

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