Fix TF2 HUD vertical viewport layout

[Hona]

Summary

• make repeated TF2 HUD viewport updates atomic and inert when unchanged
• add one measured RAF-coalesced presentation viewport owner shared by Rendering and every VGUI runtime
• handle ResizeObserver, visual viewport, orientation, fullscreen, pointer lock, DPR, zero-size suspension, and teardown
• eliminate the unexplained bottom black band across desktop, ultrawide, mobile, rotation, DPR, and restore schedules

Verification

• 291 Bun tests
• HUD layout profile
• cold/warm/mobile headed browser acceptance
• TF2 WASM verification
• VGUI browser verification
• TF2 Vite production build

No changes to user-authored playsrc/README.md.

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