Fix MPH HD and compute presentation regressions

[mstan]

Summary

• Guard compute renderer texture-size uniform updates to textured variants only
• Enable high-resolution vertex coordinates above 1x internal resolution
• Allow native-HD direct top presentation without Adaptive Widescreen
• Preserve 4:3 output for native-width direct presentation with black bars

Validation

• Windows runner build passed
• Windows runner ctest: 15/15 passed
• Linux runner ctest in MPH release build: 15/15 passed

Companion MPH prerelease branch pins this commit for v0.4.3-alpha testing.