minor interpolation fix

[JulienGaubil]

Summary

Switches the interpolation in the DPT head from nearest-neighbor to bilinear.
Uses `align_corners=True, consistent with common practice in dense geometric tasks.

Motivation

This change does not produce significant differences in quantitative performance,
but it noticeably improves spatial smoothness in dense predictions.

Notes

• No breaking changes.
• Matching behavior with typical depth/normal DPT architectures.