fix: restore native drawer layout after keyboard dismissal

[lodystage]

Related issue

Same-repository fix based on a reported HarmonyOS/Zhuoyi keyboard dismissal problem; no linked issue.

Problem / pressure

After dismissing the keyboard in an Android-compatible native shell, the conversation composer can remain suspended above a blank area. Vaul can capture the already-shrunken drawer height and restore that stale height when the viewport expands.

Summary

Native non-iOS side drawers without snap points now preserve CSS sizing and compute the bottom inset from the current visual viewport. Window resize and visual viewport resize/scroll events update the inset even when the input retains focus. iOS, bottom sheets, and explicit repositioning opt-outs retain their existing behavior.

Before / after

Before: the regression fixture restores an 800px viewport but leaves a 480px drawer height. After: the drawer has no cached inline height and the bottom inset returns to zero.

Test plan

• Nine regression tests passed using Vitest 3.2.4 with an isolated configuration and locally available dependencies; the ordinary workspace runner was blocked by broken dependency links.
• Disabling the new viewport handling reproduces the stale 480px height and leaves six regression cases failing.
• Targeted Prettier and oxlint checks, plus git diff --check, passed.
• Full component typecheck was attempted but blocked by missing workspace dependencies. Full pnpm check was not completed.
• HarmonyOS/Zhuoyi device verification remains outstanding.

Context handoff

Instructions for reviewing agents

• Review focus: Check shared drawer sizing across keyboard overlay and WebView resize modes.
• Decisions to challenge: Validate replacing Vaul repositioning only for native non-iOS side drawers without snap points.
• Plausible failures / evidence gaps: Device-specific viewport event ordering and nested drawer behavior need real-device verification.

Authoring context

• User goal / directives: Restore composer layout after keyboard dismissal in HarmonyOS/Zhuoyi.
• Constraints / non-goals: Keep the change in shared public UI; preserve existing iOS and bottom-sheet behavior.
• Risk-bearing decisions: Use live viewport occlusion rather than cached height or input focus to drive side-drawer positioning.
• Destructive or irreversible behavior: No data mutations, migrations, or destructive actions are introduced.
• Deliberately not done or tested: No native application changes or device tests; the native shell is outside this repository.
• Unknowns / confidence: Deterministic regression coverage passes; actual device event delivery remains unverified.