Finish native recovery and client acceptance

[ChanTso]

Delayed conversation history could replace a newer completed iOS reply. Recovery now checks the originating chat generation, and the regression waits for the old history task to finish. Checkout confirmation also stays in the cart until creation succeeds; both native clients explain stale cart/quote conflicts in Chinese. Saved preference values retain the user's language.

Adds a separate SwiftUI streaming replay scheme using the shared decoder and real conversation view, with XCTest process metrics and rendered frame attachments. Updates client documentation to reflect the implemented Android/iOS buyer features. No public business deployment or database migration.

Validation:

• Python lint/format and full enabled-runtime suite: 977 passed, 1 skipped.
• Web typecheck, 39 tests and production build passed.
• Android shared JVM/unit tests, APK and lint passed; 3 connected tests passed on API 36 after rerunning an initial emulator teardown/disconnect failure.
• iOS: 11 native tests passed. Separate native streaming replay passed; results are simulator/process measurements, not FPS or physical-device capacity.
• Real Java/MySQL: all 6 buyer integration tests and the merchant prepare/approve/conflict/replay test passed. An additional overview-read test failed its legacy fixed 87-product fixture assertion because the current demo has 88 roots including a limited-release product; no test was weakened and no fixture was reset.
• Native manual acceptance: same-account cart updates and rejected stale checkout; iOS checkout/payment/refund with Android readback; terminate after Java cart commit and explicitly recover the original request with SQL showing one applied add. Real model preference extraction produced Chinese and persisted history.
• Independent read-only review completed with no blocking findings.

The local iPhone is offline; physical-device interaction/performance acceptance is not claimed. The published Pages site is unchanged.