Do not treat pinch zoom as keyboard contraction

[Chris0Jeky]

Purpose

Take #1867 item 1 as a bounded, stacked policy decision. useVisualViewport treated every VisualViewport resize identically, so browser pinch zoom (scale > 1) shrank and offset CardModal/TdDialog exactly like a software keyboard.

The rule is now explicit:

• at scale 1, follow visualViewport.height and offsetTop as before;
• above scale 1, let browser zoom own navigation and use the caller's existing fallback;
• layout callers expose window.innerHeight / 0px;
• unset callers remove the custom properties so their CSS dvh/vh ladder remains authoritative;
• returning to scale 1 resumes visual-viewport geometry on the next event.

Red → green evidence

RED — exact test-only head. Commit b5affc810ec4f660f8d12103113fe0b94db4782a added only useVisualViewportPinchZoom.spec.ts. CI run 34916243641, Ubuntu frontend job 104214661061, passed lint, typecheck, production build, and PWA validation, then failed the frontend test phase. Its archived JUnit receipt contains exactly two failures, both in the new spec:

• layout caller: received 260px, expected 900px;
• unset caller: received 260px, expected an absent custom property.

No unrelated frontend test failed.

GREEN candidate. Commit 5f13a9f94d5db7dc8ee0b3c280aa62b4eae40d67 adds the scale-aware classification and documents the policy. Its exact-head hosted matrix is the evidence gate; this PR remains draft until that matrix completes and because it is stacked on #3104.

Scope

• Pinch-zoom classification only.
• No dialog CSS, CardModal layout breakpoint, keyboard-contraction, fallback-resize, focus, or server behavior changes.
• Stacked on Refresh CardModal fallback height on window resize #3104 because both touch the same composable; merge/retarget that parent first.
• [Frontend] TdDialog/useVisualViewport residuals: pinch-zoom scale, prefix validation, ungated geometric E2E (PR #1864 review) #1867's separate gated-geometric-E2E question remains open.

Refs #1867