fix(proof): fail fast on bluetooth off

[trancee]

Summary

• Added a shared Bluetooth preflight check to the proof app so GATT runs fail fast when BluetoothManager, BluetoothAdapter, or Bluetooth enabled state are unavailable.
• Routed the preflight failure into both the app UI state and logs, replacing the opaque BluetoothGattServer is unavailable crash with a clearer diagnostic.
• Updated the direct-proof docs, device matrix notes, and developer best-practices guidance to reflect the Bluetooth-off NAM-LX9 quirk and the new visible preflight state.

Verification

• ./gradlew verifyDocs
• :meshlink-proof:android:connectedDebugAndroidTest for the Bluetooth contract test
• direct-proof regression suite for the GATT contract passed
• targeted GATT-primary rerun confirmed timings.transportMode = GATT and narrowed the blocker to Bluetooth being off on the passive device

Branch

• gatt-bluetooth-preflight

Latest commit

• a1598d8 docs(explanation): add bluetooth readiness best practice