Fix mobile empty-editor layout + hint copy on touch devices (0.9.2)

[Digidai]

Summary

• remove the mobile empty-editor height clamp (clamp(320px, 56dvh, 520px)) and make the editor sheet fill the available viewport height under the top bar
• stop reserving full completion-bar space on mobile when no ghost suggestion is visible; keep the larger bottom gap only when .completion-visible is active
• make mobile hint copy context-aware: empty/no-ghost state no longer mentions Accept, while ghost-visible state still does
• bump version metadata to 0.9.2 (package.json, package-lock.json, src/version.js) and add changelog entry
• add targeted regression tests covering:
  • mobile hint text rules for empty vs ghost-visible states
  • completion bar visibility guard still requiring state.ghost
  • mobile CSS viewport fill + conditional bottom spacing and desktop A4 min-height guard

Validation

• npm test
• npm run check