fix(web): keep select poppers inside collision bounds

[XiaoSeS]

What

Keep shared Select popper content inside Radix collision bounds on small viewports.

Why

The previous shared Select fix added viewport-based max height, but the component still applied Tailwind translate utilities after Radix calculated the collision boundary. On short browser windows, that static transform could move the menu a few pixels outside the viewport.

This is visible in long Select menus such as the publish namespace picker.

How

• Move the default popper gap to Radix sideOffset={4}.
• Remove static translate-* side transforms from SelectContent.
• Add a contract test so the shared Select does not reintroduce static popper transforms.

Testing

• pnpm exec vitest run src/shared/ui/select.test.ts
• pnpm run typecheck
• pnpm run lint
• Local release Compose preview built and started from the exact SHA.
• Manual validation passed on the publish namespace picker with 30 seeded namespaces.

Impact

• Frontend-only shared UI fix.
• No API, schema, backend, scanner, migration, or deployment-chain change.