️🛠 - Mobile CI target for feature-flagged compilation

[maxwellmattryan]

Description

Add continuous integration checks to ensure the mobile Rust target continues to compile as desktop development proceeds. Without CI validation, desktop PRs will silently break mobile compilation by introducing desktop-only code in shared modules.

Scope:

• Add a GitHub Actions job that runs on every PR touching src-tauri/:
  • cargo check --target aarch64-apple-ios --no-default-features --features mobile
• Optionally add Android target check (requires Android NDK in CI):
  • cargo check --target aarch64-linux-android --no-default-features --features mobile
• Install required Rust targets in CI: rustup target add aarch64-apple-ios aarch64-linux-android
• Ensure the CI job fails fast and provides clear error messages indicating which code broke mobile compilation

Dependencies: Requires #48 (feature-flag desktop-only code) to be complete first.

Key files:

• .github/workflows/ — new or updated workflow file
• src-tauri/Cargo.toml — feature flags (from ️🛠 - Feature-flag desktop-only Rust code for mobile compilation #48)

Open questions

• Should this be a separate workflow or added to an existing CI workflow?
• Is the Android NDK available in GitHub Actions macOS runners, or does it need explicit setup?
• Should the CI also run cargo test for mobile target, or just cargo check?

Acceptance criteria

• GitHub Actions runs cargo check for iOS mobile target on every PR that modifies src-tauri/
• PRs that break mobile compilation are flagged before merge
• CI passes for the current codebase after feature-flagging (️🛠 - Feature-flag desktop-only Rust code for mobile compilation #48) is complete
• CI job runs in under 5 minutes

Tasks

TBD