[kev1n77]

Summary

Fix the gap between the sidebar and the lower-left rounded corner of the welcome scene on Windows. Fade only the welcome content, keeping the opaque scene background out of the opacity animation's composited layer. Preserve the existing corner radius, fade timing, and reduced-motion behavior.

Type and Areas

Type: Bug fix

Areas: Web UI; Windows desktop rendering

Motivation / Impact

In the native WebView2 host, the welcome scene's background opacity animation clears the sidebar material outside the shell's rounded clip. The gap disappears when opening settings and returns when closing the last tab. Keeping the background static prevents the transparent cutout.

Verification

• Reproduced using an isolated Windows desktop debug host with the installed release frontend. Injected CSS compiled from the changed SCSS for the fix comparison; no installer rebuild was performed.
• Verified welcome → settings → close settings → welcome, plus hovering the navigation divider. The original welcome state had 348 fully transparent pixels in the captured corner region; the patched state had zero, including after navigation and hover.
• Verified reduced-motion rendering in Chromium: the welcome root, content, and cursor all report no animation.
• Passed: pnpm run type-check:web, pnpm run theme:visual-contract, and git diff --check.
• Ran: pnpm run motion:audit (intent-review inventory).
• pnpm run check:web is blocked by the existing stale MiniApp chat-styles.css projection reported by scripts/generate-miniapp-chat-styles.mjs --check. The changed welcome stylesheet is outside that projection's inputs.
• Remote workspace, Remote Control, Peer Device Mode, and Detached Dispatch were not exercised.

Reviewer Notes

AI-assisted implementation. Testing level: focused native rendering and navigation verified; the complete repository frontend gate remains blocked as described above. No persisted data, protocol, or product logic changes.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable (not applicable to this CSS-only fix).