feat(app): wire missing fe/be flows

[risu729]

Summary

• add typed app mutations for profile updates, avatar uploads, and POI visits
• replace profile demo values with live user, progress, quest, perk, and saved-sticker data
• persist username and avatar edits through the API and wire sign-out
• add web and native POI check-in actions using the current Expo Location position
• render the persisted avatar on both web and native maps

Rebase update

• rebased onto the latest main
• preserved the current location-permission HUD and platform-specific map structure
• removed the old native fallback that could submit POI coordinates when no user position was available
• kept automatic geofence entry as follow-up work in PLAN.md

Checks

• bun run check
• bun run build:app