fix: prevent refresh flicker by using deferred clear instead of immediate terminal clear

[linw1995]

This PR prevents refresh flicker in the terminal UI by using deferred clear instead of immediate terminal clear operations.

Changes:

• Replace immediate terminal clear with deferred clear mechanism
• Improves UI responsiveness during refresh operations

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 51.72%. Comparing base (e5977ab) to head (038f635).
⚠️ Report is 10 commits behind head on dev.

Files with missing lines	Patch %	Lines
crates/coco-tui/src/app.rs	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #107      +/-   ##
==========================================
- Coverage   53.46%   51.72%   -1.74%     
==========================================
  Files          88       91       +3     
  Lines       21248    23376    +2128     
==========================================
+ Hits        11360    12092     +732     
- Misses       9888    11284    +1396     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.