Fix CargoKit plugin detection for current Flutter Android builds

[Xare123]

Problem

CargoKit can silently skip or hang native plugin builds when Flutter plugin class names and target-platform properties differ from older assumptions. A green APK may then omit required Rust native libraries.

Change

Handle direct Flutter project/plugin detection safely, propagate target platform consistently, patch affected pub-cache CargoKit copies idempotently, and assert every required native library exists in the APK.

Validation

• workflow YAML and Bash syntax pass
• patcher passes a two-run idempotence fixture
• git diff --check and scope checks pass

Scope and sequencing

No sampler, Windows, signing, or Cloud Sync behavior. This branch is independently based on rustpush; CI execution is expected to provide the full APK proof and it can land after the CI modernization draft.