Initialize Tauri iOS support with conditional compilation:
- Desktop-only features (git CLI, menu, MCP, Claude CLI) gated behind #[cfg(desktop)]
- Mobile stubs return graceful errors so frontend degrades smoothly
- Vault read/write, AI chat, search, settings work unchanged on both platforms
- Xcode project generated, Rust cross-compiles cleanly to aarch64-apple-ios-sim
- All 581 Rust tests and 2201 frontend tests still pass
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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