Mobile App & UX Upgrades

[7086cmd]

Mobile app upgrades for user experience, positioning, and cross-platform reach.

Tasks:

• Fix merchant data loading bugs
• Add calibratable RSSI parameters for RNSS
• Extract indoor positioning to reusable module
• UI upgrades (visual route overlays, multi-floor nav, secure unlock)
• Multi-language support expansion
• Offline-first improvements

Details in README and CRITICAL_TODOS.md