fix(css): stabilize scoped rosview styling

[joaner]

Restore scoped preflight behavior for standalone and embedded builds, and isolate playback scrubber centering from host Tailwind transforms for v1.5.3.

Description

• Add standalone.css for the SPA shell (html / body / #root margin and full-viewport sizing) without leaking global resets into the npm library bundle.
• Extend scoped preflight under #rosview-root: typography/list/fieldset margin resets, form control border normalization, and Tailwind .border* utility initialization so shadcn-style borders render correctly with preflight: false.
• Fix #rosview-root layout: explicit root dimensions plus an inner h-full w-full wrapper so Tailwind utilities scoped with important: '#rosview-root' apply to descendants, not only to the root element itself.
• Fix standalone App.tsx outer shell to use inline viewport sizing instead of scoped w-screen / h-screen classes outside #rosview-root.
• Fix embedded playback scrubber: replace -translate-x/y-1/2 utilities with ros-playback-center-x / ros-playback-center-xy and translate: none so host apps using Tailwind v4 do not double-apply translate (thumb offset + broken track hit-testing).
• Bump package version to 1.5.3.

Motivation / related issue

After v1.5.2 scoped CSS (important: '#rosview-root', preflight: false):

1. Standalone site — Missing base resets (body, p margins, visible .border on buttons) made the main site look broken compared to pre-1.5.x.
2. Embedded hosts (e.g. limx-agent) — Playback thumb appeared too high and scrubbing failed because the host’s global Tailwind v4 translate utilities stacked on top of rosview’s transform-based centering, and pointer-events-none overlays no longer hit #playback-track.

This PR restores predictable styling in both modes without re-enabling global preflight that would affect the host page.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing behavior to change)
• Documentation update
• Refactor / internal cleanup (no behavior change)

Checklist

• npm run lint passes with no errors
• npm test passes (unit tests)
• npm run build and npm run build:lib succeed
• New behavior is covered by tests (or explain why tests aren't applicable)
• Documentation updated (README, API.md, EMBEDDING.md) if the public API changed
• Breaking change: all affected call sites updated and migration path described in PR description

Tests: Visual/CSS integration fix; no new unit tests. Manually verified standalone localhost:5173 and embedded /visualize playback track centering and scrubber hit-testing.

API compatibility

N/A — no changes to src/entrypoints/index.ts exports. CSS-only and internal component structure changes; consumers should upgrade to @ioai/rosview@1.5.3 and continue importing @ioai/rosview/style.css once published.

Screenshots / recordings