feat: add relay health browser screen

[barrydeen]

Summary

• New Relay Health screen accessible from Settings in the navigation drawer
• Shows all relays (persistent, DM, ephemeral) with real-time connection status, relay icons (via NIP-11 prefetch), and operator profiles
• Displays inbox author coverage from the scoreboard with overlapping profile pictures (matching the "covers N" data from the feed relay picker)
• Shows cooldown reasons (from console log failure entries) and bad relay reasons (zero-event sessions, disconnects, rate limits)
• Supports sorting by status/failures/events/name and filtering by all/bad-only/errors-only
• Tapping a relay navigates to the existing RelayDetailScreen for a deep dive

Changes

• New: RelayHealthScreen.kt — health dashboard UI
• New: RelayHealthViewModel.kt — aggregates data from RelayPool, RelayHealthTracker, RelayScoreBoard, RelayInfoRepository, and EventRepository
• Modified: RelayHealthTracker.kt — exposed session history/active sessions, added bad relay reasons tracking
• Modified: RelayPool.kt — added getEphemeralRelayUrls() and getAllRelayUrls()
• Modified: RelayDetailScreen.kt — made format helpers internal for reuse
• Modified: Navigation.kt, FeedScreen.kt, WispDrawerContent.kt — wired up route and drawer item

Test plan

• Drawer shows "Relay Health" item under Settings
• Screen loads with all relays listed with icons and connection status dots
• Relay icons load (not just fallback letters)
• Inbox author profile pictures appear for scored relays
• Bad relays show reason text (e.g. "8/10 sessions received 0 events")
• Cooldown relays show reason text from last failure
• Sorting and filtering chips work
• Tapping a relay navigates to RelayDetailScreen
• Stats update every ~2 seconds