[codex] Phase 3G: chat UI polish

[sukar0972]

Summary

Phase 3G applies a narrow web UI polish slice:

• restore the ultrathink composer frame border effect
• stabilize composer provider chrome while typing by deriving a coarse prompt-injection state
• add a small regression assertion documenting that ordinary prompt body edits stay in the same ultrathink state

Intentionally deferred from this phase

• RightPanelTabs middle-click/inset commits: this fork currently uses RightPanelSheet and does not have the upstream tabbed right-panel store/component path.
• Main sidebar toggle: conflicts broadly across fork-customized layout/keybinding files; should be a separate focused PR if we still want it before Phase 4.
• Persistent word-wrap: pulls in deleted desktop/file-preview paths plus larger ChatMarkdown/DiffPanel refactors; better grouped with the markdown/scroll UI phase.

Grok Composer 2.5 review

Reviewed with grok -m grok-composer-2.5-fast.

Verdict: approve, no merge-blocking issues. I applied Grok's small non-blocking suggestion to add a stabilization-contract assertion and a comment explaining why the raw prompt became a coarse enum.

Verification

• vp test apps/web/src/components/chat/composerProviderState.test.tsx — 10 passed
• vp run typecheck — passed
  • existing suggestion remains: src/diagnostics/ProcessResourceMonitor.ts(315,5)
• vp check — passed
  • existing react(no-unstable-nested-components) warnings remain