feat(03-01): create OverlayService and add retry dependency
- Add retry package (^3.1.2) for robust platform operations
- Create OverlayService wrapper for all FlutterOverlayWindow calls
- Implement showOverlay/closeOverlay with 3-attempt retry logic
- Add shareData fire-and-forget with warn-level logging
- Add isActive, overlayListener, checkPermission helpers
- Define staleness constants: 3s dim, 10s dash, 0.5 opacity, 1s check
- Define GPS_GRACE_PERIOD constant (30 seconds)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Mikkeli Matlock
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