chore: polish chat UI

[appflowy]

Feature Preview

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PR Checklist

• My code adheres to AppFlowy's Conventions
• I've listed at least one issue that this PR fixes in the description above.
• I've added a test(s) to validate changes in this PR, or this PR only contains semantic changes.
• All existing tests are passing.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.62%. Comparing base (94f9349) to head (c7e5df0).
Report is 793 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##            main    #5533       +/-   ##
==========================================
+ Coverage   9.70%   86.62%   +76.92%     
==========================================
  Files        685      219      -466     
  Lines      31812     5039    -26773     
  Branches       0      833      +833     
==========================================
+ Hits        3086     4365     +1279     
+ Misses     28726      565    -28161     
- Partials       0      109      +109     

Flag	Coverage Δ
appflowy_flutter_unit_test	?
appflowy_web_app	86.62% <ø> (?)

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