fix(web): align AskUserQuestion interaction

[LIUXIN557]

Summary

• replace the composer with the pending AskUserQuestion picker on home and session surfaces
• render persisted submitted and cancelled answers from durable result metadata
• apply theme accent colors to selected options and primary submission actions
• localize the cancellation result and document the agreed interaction behavior
• add architecture and layout regression coverage

Verification

• \pnpm --dir C:\dev\acecode\web test\
• \pnpm --dir C:\dev\acecode\web build\
• \git diff --check\

Notes

• Existing unrelated working-tree changes to the mdast compatibility patch and \web/pnpm-lock.yaml\ were intentionally excluded from commit \f475537.