feat(mobile): scaffold native iOS shell

[wgqqqqq]

Based on 1.0.0-explore.

Scope

This PR establishes the native iOS shell for BitFun. It is a foundation for continued iOS development, not a claim of full iOS feature parity or production completeness.

Included

• SwiftUI application entrypoint and Xcode project.
• HarmonyOS-aligned conversation shell, drawer, settings surface, chat timeline, and composer.
• KMP BitFunMobileCore adapter boundary for local chat, pairing, account login, and remote-session state.
• Initial account flow that selects an online DESKTOP-* device before creating a remote session.
• Xcode 16.4 build instructions using ~/Downloads/Xcode.app.
• iOS Argon2 cinterop annotation required by the shared crypto build.

Verification

• pnpm run mobile:architecture
• git diff --check
• Xcode 16.4 signed simulator build succeeded
• Installed and exercised on the iPhone 16 Pro simulator

Credentials were not written to the source code, commit, or pull request.