refactor(mobile): replace QR pairing with account sign-in

[wgqqqqq]

Summary

• Replace the mobile QR / pairing-link connect flow with account sign-in. Android, iOS, and HarmonyOS now list the desktops of the signed-in account and connect from a device picker, so a temporary scan pairing is no longer the entry point.
• Consolidate mobile settings into one sheet per platform: a new current-control section and a remote-permission section replace the separate general/remote settings surfaces.
• Drop the camera and scanner stack that only served pairing: Android camera-* and ML Kit dependencies plus the CAMERA manifest entries, iOS NSCameraUsageDescription, and HarmonyOS ohos.permission.CAMERA. HarmonyOS ohos.permission.READ_PASTEBOARD goes too, because the pasteboard read path and its runtime permission request were the pairing-link paste; ClipboardService keeps only the mini-app writeText path, which needs no permission.
• Move the HarmonyOS i18n catalogues, native string resources, the iOS project file, and the HarmonyOS architecture contract's required presentation files with the same change.

Deleted: InlineQrScanner/InlineQrDecoderTest/pairing-qr.png/AccountScreen/ConnectView/GeneralSettingsScreen/OtherConnectionSection/SignedOutConnectionActions (Android), PairingSheet/QRCodeScannerView (iOS), ConnectManualPairingOverlay/RemoteControlSettingsSheet/InlineQrScanner/QrScanService/ConnectScanDecisionPolicy/RemoteControlSettingsPagePolicy/welcome_scan.svg (HarmonyOS).
Added: AccountLoginScreen.kt, AccountDevicePickerSheet.swift, AccountLoginSheet.ets, CurrentControlSection.ets, RemotePermissionSection.ets, SettingsPagePolicy.ets.

Validation

Run on macOS against the pushed commit; the Android and HarmonyOS toolchains were the bundled JBRs from Android Studio / DevEco Studio.

• git diff --cached --check — passed
• pnpm run mobile:ui:check — passed
• pnpm run theme:color-audit:all — passed (24 surfaces)
• pnpm run harmony:architecture — passed
• cd src/apps/mobile/ios && ./Testing/run-pure-swift-tests.sh — passed
• cd src/apps/mobile/android && ./gradlew :app:assembleDebug :app:compileDebugAndroidTestKotlin :app:testDebugUnitTest — passed
• cd src/apps/mobile/harmonyos && node --test miniapps/*.test.cjs — 6 passed, 0 failed
• cd src/apps/mobile/harmonyos && source scripts/ohos-env.sh && "$HVIGORW" --mode module -p module=entry@default -p ohos.test.type=LocalTest test --no-daemon — Tests run: 511, Failure: 0, Error: 0, Pass: 511

Not green, and pre-existing on the base commit d4e96d430 — the same commands fail identically in a clean worktree of that commit, so they are not caused by this branch:

• cd src/apps/mobile/shared && ./gradlew jvmTest — 503 tests, 1 failed: RemoteSessionStoreTest.imageSendFailureDoesNotConsumeAttachmentsAndAckKeepsNewTyping
• cd src/apps/mobile/harmonyos && node --test tools/tests/*.test.cjs — 194 tests, 1 failed: sidebar final entry hierarchy keeps modes in workspace plus and tools in the footer
• pnpm run mobile:architecture — 4 violations (sharedReachesPlatformTrees, defaultArgsInFeatureApi); AppSidebar.ets already lacked workspaceTools.title at d4e96d430, and the reported files are untouched here

Risks

• Removes a user-facing connect path. A desktop reached only through a temporary QR pair now needs an account sign-in on both ends.
• Camera permission removal is a behaviour change on Android, iOS, and HarmonyOS; the scanners no longer exist, so the permission asks disappear with them.
• Local-only evidence. The Remote workspace, Remote control, Peer Device Mode, and Detached Dispatch scenarios from AGENTS.md were not exercised on a device or a second host.
• Existing installs keep their saved connections and persisted state; no stored shape changes in this branch.

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