[Service] Create StatsCollector and integrate with MainRepository

[LeGeRyChEeSe]

Description

Create the StatsCollector service that orchestrates statistics collection and sending, as well as its integration into MainRepository.

File to create

• app/src/main/java/com/vrhub/data/StatsCollector.kt

Service API

Method	Description
collectStats(installedGames, userTier)	Checks consent, builds payload and sends via StatsApiService
updateConsent(enabled)	Updates consent on the server side
getUserTier(email)	Fetches tier from /user/tier

Integration points in MainRepository

• After syncCatalog() → maybeCollectStats()
• After toggleFavorite() → maybeCollectStats()

Error handling

• Network Error → Retry max 3 (exponential backoff)
• HTTP 403 → Consent revoked server-side, stop future collections
• HTTP 5xx → Retry max 3
• Other → Log error, do not block UI

Reference

• docs/CLIENT_SPEC.md §3, §4
• docs/CLIENT_IMPLEMENTATION.md §7, §8