[Network] Implement StatsApiService and data models

[LeGeRyChEeSe]

Description

Create the network layer to communicate with the vrhub-monetization server for statistics collection.

Files to create

• app/src/main/java/com/vrhub/network/StatsApiService.kt
• app/src/main/java/com/vrhub/network/StatsModels.kt

Endpoints to implement

Method	Endpoint	Description
POST	/stats/collect	Send anonymized stats
POST	/stats/consent	Update consent status
GET	/user/tier?email=	Fetch user tier

Data models

• StatsCollectRequest — games: List<GameStat>, tier: String, timestamp: Long
• GameStat — package_name: String, is_favorite: Boolean
• StatsCollectResponse — message: String
• ConsentRequest / ConsentResponse
• UserTierResponse — email, tier, status

Integration

• Base URL from ServerConfig.monetizationUrl (fallback: https://vrhub.sunshine-aio.com)
• Add to existing Retrofit builder (Gson converter)

Reference

• docs/CLIENT_SPEC.md §4, §7
• docs/CLIENT_IMPLEMENTATION.md §3