test(examples): VRT automation for stress-tv & viewport-memory; fix shader name

[chiefcll]

What

Brings two examples into the visual-regression suite and fixes a latent shader-name bug they'd otherwise certify.

VRT automation

Adds an automation export to stress-tv and viewport-memory. Each runs test(settings), waits for the renderer to go idle (waitUntilIdle), then snapshot()s the stable final frame. Neither was covered before — the whole dense-grid / stress family had zero visual coverage.

Shader-name fix

Several examples called createShader('RoundedRectangle', …), but the registered key is 'Rounded' (examples/common/installShaders.ts). The wrong name silently fell back to the default shader — so "rounded" rectangles rendered with square corners, and circles rendered as squares. Adding a VRT for viewport-memory without this fix would have certified the bug. Corrected across all occurrences:

• viewport-memory.ts (4×) — its red/blue/yellow circles and green rounded rects
• mount-pivot.ts (2×)
• scaling-animations.ts
• text-events.ts

None of these are currently in VRT, so no existing certified snapshot changes.

Verified in-browser

• viewport-memory now renders true circles and rounded corners, no ShaderType not found warning (before: squares).
• stress-tv renders unchanged after its default function was renamed to test (so the new automation export can drive it); interactive remote controls untouched.

Notes for reviewer

• CI snapshots to be captured manually (pnpm test:visual:update-ci, Docker) — as agreed.
• RoundedRectangle → Rounded is the same latent bug originally flagged for viewport-memory; fixed everywhere it appears in the examples while here.

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