refactor: unify prompt template system and add base branch support

[CarlJi]

No description provided.

[CarlJi]

🤖 代码审查结果

[codecov]

Codecov Report

❌ Patch coverage is 0% with 55 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@558f50c). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
internal/context/template_generator.go	0.00%	36 Missing ⚠️
internal/modes/tag_handler.go	0.00%	10 Missing ⚠️
internal/modes/review_handler.go	0.00%	9 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #342   +/-   ##
=======================================
  Coverage        ?   12.41%           
=======================================
  Files           ?       57           
  Lines           ?    11361           
  Branches        ?        0           
=======================================
  Hits            ?     1411           
  Misses          ?     9802           
  Partials        ?      148           

Flag	Coverage Δ
unittests	12.41% <0.00%> (?)

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