Per-eye vergence data not available through XR_ANDROID_eye_tracking (combined gaze only)

## Summary

When using eye tracking via the `XR_ANDROID_eye_tracking` OpenXR extension on Samsung Galaxy XR, the left and right eye gaze data appear to be identical (combined/averaged gaze duplicated to both eyes). We need independent per-eye rotation data to measure binocular convergence (near point of convergence).

## Use Case

We are building a clinical neurologic exam app (SDNE) that includes a fixation/convergence assessment task. Convergence measurement requires computing the vergence angle between the two eyes as a target approaches the patient. Without independent left/right eye pose data, this measurement is impossible.

## What We Observe

- `EyeTracking.LeftEyeRotation` and `EyeTracking.RightEyeRotation` return values that appear identical or nearly identical
- Combined gaze direction works well for saccades, pursuit, and fixation tasks
- Confidence is reported as 0.95 (hardcoded?)
- Device: Samsung Galaxy XR (SM_I610)
- Unity 6 (6000.3.6f1) with OpenXR

## Questions

1. Does the `XR_ANDROID_eye_tracking` extension support per-eye vergence data on Galaxy XR?
2. If so, is there a specific permission, API path, or extension that must be enabled to get independent left/right eye poses rather than combined gaze?
3. If not currently supported, is this planned for a future SDK release?

## Environment

- Device: Samsung Galaxy XR (SM_I610)
- OS: Android XR
- Unity: 6000.3.6f1
- OpenXR runtime
- Permissions granted: `EYE_TRACKING_FINE`, `EYE_TRACKING_COARSE`

Start by reviewing the XR_ANDROID_eye_tracking behavior and the Unity OpenXR EyeTracking.LeftEyeRotation and RightEyeRotation values on Samsung Galaxy XR with the listed permissions. Determine whether independent per-eye poses are supported, require another API or permission, or are unavailable; document the confirmed SDK behavior and any required next step.

Written by the indexing model from the issue text.