Phase 1b: Extract ClientUpdateStrategy and UpgradeUpdateStrategy from Bootstrap

[JusterZhu]

Goal

Per section 2.3 of the v2 plan, create role-based strategy classes:

• ClientUpdateStrategy — extracts LaunchClientAsync from Bootstrap
• UpgradeUpdateStrategy — extracts LaunchUpgradeAsync from Bootstrap

This completes the 3-role strategy system:

• ClientUpdateStrategy (AppType.ClientApp)
• UpgradeUpdateStrategy (AppType.UpgradeApp)
• OSSUpdateStrategy (AppType.OSSApp) ✅ done in refactor: Phase 1 — role-based OSS strategy, built into unified Bootstrap (#352) #353

Part of GeneralUpdate v2 refactoring plan.