Refactor with parent interaction id

[wanglam]

Description

1. Pass empty executor memory when PER Agent execution, speed up the first step display
2. Using parent interaction id to fetch PER Agent execution result
3. Only polling task when paragraph result no messageId and executorMemoryId

Issues Resolved

[List any issues this PR will resolve]

Check List

• New functionality includes testing.
  • All tests pass, including unit test, integration test and doctest
• New functionality has been documented.
  • New functionality has javadoc added
  • New functionality has user manual doc added
• Commits are signed per the DCO using --signoff

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[codecov]

Codecov Report

❌ Patch coverage is 76.31579% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.07%. Comparing base (fd3b5b7) to head (7632158).

Files with missing lines	Patch %	Lines
...s/deep_research/services/per_agent_task_service.ts	0.00%	4 Missing ⚠️
...eep_research/services/per_agent_message_service.ts	92.30%	2 Missing ⚠️
server/services/ml_service.ts	33.33%	2 Missing ⚠️
public/utils/ml_commons_apis.ts	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #105      +/-   ##
==========================================
+ Coverage   64.78%   65.07%   +0.28%     
==========================================
  Files          57       58       +1     
  Lines        1806     1841      +35     
  Branches      444      447       +3     
==========================================
+ Hits         1170     1198      +28     
- Misses        634      641       +7     
  Partials        2        2              

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