feat: action-panel block

[zyx1121]

For pages whose whole job is one action, starting with portal's door page (today a 160px native emoji button with hand-made phases).

• ActionPanel: one 192px round primary button with an optional icon and a text-title verb, for app-shell's spotlight layout.
• Phases: ready, pending (開門中…, locked), done (success fill with doneLabel for resetAfter ms), back to ready; a throw returns to ready for the caller's toast.
• disabledReason greys it out and says why under it.
• Press scales to 95%, dropped under reduced motion.
• CI smoke installs the block.

Verified on sandbox with WebKit, light and dark: 開門 → 開門中… (disabled) → 已開門 → 開門 after 3s.

Found while building: cn treats text-title / text-body as colors and drops them next to a text color; this block wraps the label in its own span. The registry-wide fix follows in a separate PR.

🤖 Generated with Claude Code