#14 Add native camera-permission handling (no third-party package needed)

[LahaLuhem]

New public API

• TextSightController.requestCameraPermission() — drives the system prompt when undecided
• TextSightController.checkCameraPermission() — prompt-free status read (e.g. to gate a priming screen)
• CameraPermissionStatus { granted, denied, permanentlyDenied }

start() and all existing APIs are unchanged.

Native

• iOS — AVCaptureDevice.requestAccess (system frameworks only).
• Android — plugin is now ActivityAware with a RequestPermissionsResultListener;
  distinguishes denied (re-askable) from permanentlyDenied via shouldShowRequestPermissionRationale.

Also

Pigeon control channel extended + regenerated; example migrated off permission_handler
(dependency removed); README permission section rewritten; unit tests for the new methods.
Consumers still declare NSCameraUsageDescription (iOS); the Android CAMERA manifest entry
ships with the plugin.

closes #14