refactor: scheduled task splitting

[withchao]

🔍 What type of PR is this?

👀 What this PR does / why we need it:

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

🅰 Which issue(s) this PR fixes:

Fixes #1298

📝 Special notes for your reviewer:

🎯 Describe how to verify it

📑 Additional documentation e.g., RFC, notion, Google docs, usage docs, etc.:

[sweep-ai]

Apply Sweep Rules to your PR?

• Apply: Leftover TODOs in the code should be handled.
• Apply: All new business logic should have corresponding unit tests in the tests/ directory.
• Apply: Any clearly inefficient or repeated code should be optimized or refactored.

[codecov]

Codecov Report

Merging #1299 (940a592) into main (d2f0af1) will decrease coverage by 0.03%.
The diff coverage is 0.00%.

@@           Coverage Diff            @@
##            main   #1299      +/-   ##
========================================
- Coverage   2.44%   2.41%   -0.03%     
========================================
  Files         13      13              
  Lines        778     786       +8     
========================================
  Hits          19      19              
- Misses       756     764       +8     
  Partials       3       3              

Files	Coverage Δ
pkg/common/db/relation/conversation_model.go	0.00% <0.00%> (ø)