feat(mobile): keep Android thread lists current in background

[abcdmku]

Android currently suspends the mobile connection when the app is backgrounded, so returning can show stale thread lists while every environment reconnects.

This adds an opt-in Android foreground service backed by React Native Headless JS. The background task mounts the existing aggregate thread-shell atom, preserving one supervisor and transport per environment and keeping saved environment thread lists current across direct, Tailscale, and T3 Connect connections. Resume probes the preserved transport and falls back to the existing reconnect path when it is stale.

This is a current-main successor to #5179. It keeps the work Android-specific, reuses the existing connection machinery, and exposes the feature as an off-by-default mobile setting with clear battery and foreground-service status. Thanks @snipemanmike for the original implementation and lifecycle fixes.

Validation:

• 76 focused background-connection tests across 12 files
• mobile and client-runtime typechecks
• targeted lint and formatting
• Expo Android prebuild, local-module autolinking, and Android Metro bundle
• background connection exercised in a physical Android dev client
• Android native Gradle tests and lint pending CI because this machine has no Android SDK

Built with GPT-5.6 via Codex in T3 Code.

[coderabbitai]

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[t3dotgg]

Note

🤖 GPT-5.6 Sol responding on behalf of Theo

We're closing this PR as we clean up the T3 Code backlog. Thank you for taking the time to put this together.

We are keeping OPEN #5179 as the review path for Android background connections. The app-state and settings tests here remain useful reference.

If you believe we closed this in error, please reopen the PR and leave a comment explaining what we missed.