refactor: merge GeneralClientBootstrap into GeneralUpdateBootstrap via AppType (#344)

[JusterZhu]

Summary

Eliminates the \GeneralClientBootstrap\ / \GeneralUpdateBootstrap\ duality. All client-side functionality is merged into \GeneralUpdateBootstrap, dispatched by \AppType\ (ClientApp vs UpgradeApp).

Changes

GeneralUpdateBootstrap (unified)

• LaunchAsync() dispatches by AppType:
  • \AppType.ClientApp\ → \LaunchClientAsync()\ — Bowl mgmt, custom options, dual version validation, CheckFail, ProcessInfo IPC, Silent mode, StartApp
  • \AppType.UpgradeApp\ → \LaunchUpgradeAsync()\ — receive ProcessInfo, apply updates, StartApp
  • Default (not set) → Client for backward compatibility
• New public API: \AddListenerUpdatePrecheck(), \AddCustomOption()\
• New private methods: \CallSmallBowlHome(), \ExecuteCustomOptions(), \CheckFail(), \CanSkipClient()\

GeneralClientBootstrap

• Marked [Obsolete]\ with migration guidance
• Source preserved for backward compatibility — existing code compiles with deprecation warning

Verification

• \dotnet build src/c#/GeneralUpdate.slnx\ → 0 errors, 0 warnings
• All 11 projects compile successfully
• GeneralClientBootstrap still compiles (Obsolete warning only)

Migration Guide

`csharp
// Before
new GeneralClientBootstrap().SetConfig(cfg).LaunchAsync();

// After
new GeneralUpdateBootstrap()
.Option(UpdateOptions.AppType, AppType.ClientApp)
.SetConfig(cfg)
.LaunchAsync();
`

Closes #344