Integrate reviewed visual and first-run improvements

[hamzamerzic]

Summary

This integration lands the reviewed visual/UI queue together so GitHub can validate the combined shell once rather than serially retesting seven overlapping branches.

• keep Send, Steer, and Stop continuously visible while making an optimistic queued Send become an actionable Steer immediately
• add expandable active-goal progress in the chat footer
• dismiss chat image previews with browser/gesture Back
• add current cross-platform PWA installation guidance
• start genuinely fresh workspaces in Standard mode while keeping Builder fixtures explicit
• support OpenAI Apps SDK UI icons in mini-app compilation and authoring guidance
• keep a fast first send pinned by ignoring the browser's initial non-return pageshow and initializing empty-chat scroll identity before the transcript mounts

Reconciliation

The composer work combines #292 and #294 deliberately: the optimistic queue lifecycle from #292 now uses #294's single stable primary-action identity and no opacity-zero transition. This avoids landing two mutually overwriting implementations.

The branch also carries the first-boot route/renderer alignment, explicit Builder test setup added after #288's original hosted E2E failure, and the hosted-run corrections that make first-chat failure, navigation, and Steer→Stop checks exercise their current reachable states. The final hosted trace exposed the first-send reset at the owning lifecycle seam: the empty state had no scroll node, so identity initialization was deferred until after the pin was armed. Identity now initializes before that intentional early return.

Supersedes #285, #287, #288, #291, #292, #293, and #294 after merge. #286 has already landed independently.

Testing

• frontend library suite: 2,026 passed
• frontend hook suite: 63 passed
• production/PWA build passed
• focused reconciled composer tests: 25 passed before the full suite
• git diff --check

Co-authored-by: Möbius Agent mobius-agent@users.noreply.github.com