Flutter OPPO Background GPS Tracking Demo

Brief Requirement:
Build a Flutter demo for OPPO phones only, stable GPS location under lock screen, background run & extreme power saving mode (system cannot kill tracking service).

Deliverables:
1. Full reusable Flutter source code
2. Installable test APK
3. Continuous positioning test log

Acceptance Rule:
If positioning fails to keep running under OPPO power saving & locked screen, full milestone refund.

Cost Agreement:
Total budget: $60, 3 business days delivery. This demo fee will be fully deducted from Phase 1 full 5 Android devices adaptation budget later, no extra hidden fees for location module.