feat(github): support github app auth

[wwcchh0123]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 16.38514% with 495 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@6e22b19). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
internal/github/client_manager.go	0.00%	113 Missing ⚠️
internal/modes/tag_handler.go	0.00%	87 Missing ⚠️
internal/context/collector.go	0.00%	52 Missing ⚠️
internal/github/auth/app_authenticator.go	42.68%	43 Missing and 4 partials ⚠️
internal/mcp/servers/github_comments.go	0.00%	32 Missing ⚠️
internal/github/auth/factory.go	55.00%	20 Missing and 7 partials ⚠️
internal/modes/agent_handler.go	0.00%	27 Missing ⚠️
internal/mcp/servers/github_files.go	0.00%	26 Missing ⚠️
internal/config/config.go	0.00%	21 Missing and 4 partials ⚠️
internal/modes/review_handler.go	0.00%	24 Missing ⚠️
... and 4 more

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #314   +/-   ##
=======================================
  Coverage        ?   10.98%           
=======================================
  Files           ?       42           
  Lines           ?     8937           
  Branches        ?        0           
=======================================
  Hits            ?      982           
  Misses          ?     7881           
  Partials        ?       74           

Flag	Coverage Δ
unittests	10.98% <16.38%> (?)

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[CarlJi]

这是哪里的要求？