feat: add NIP-38 user status for desktop and mobile

[wesbillman]

Summary

• Implements Slack/Discord-style user status using NIP-38 (kind:30315) parameterised replaceable events
• Desktop: status dialog with emoji picker and presets, live display in profile popovers and sidebar, fetch-then-subscribe with TanStack Query
• Mobile: bottom sheet with emoji grid and quick presets, status in settings page and member list, Riverpod cache with WS subscription and 120s backstop refresh
• Both platforms produce identical wire-format events (d=general, content=text, ["emoji", value] tag)

Details

Desktop (10 files: 2 new, 8 modified)

• features/user-status/hooks.ts — useUserStatus / useSetUserStatus hooks with fetch-then-subscribe and optimistic updates
• features/user-status/ui/SetStatusDialog.tsx — dialog with emoji picker, text input, presets, clear
• ProfilePopover.tsx — shows own status with click-to-edit
• UserProfilePopover.tsx — shows other users' status
• AppSidebar.tsx / AppShell.tsx — status display and dialog entry points
• relayClientSession.ts — subscribeUserStatuses() for live WS updates
• types.ts / kinds.ts — NIP-38 type and kind constant

Mobile (8 files: 4 new, 4 modified)

• user_status.dart — immutable UserStatus model with fromEvent factory
• user_status_cache_provider.dart — Notifier<Map<String, UserStatus?>> with WS subscription, batched fetch, 120s backstop
• user_status_provider.dart — AsyncNotifier<UserStatus?> for own status with optimistic publish
• set_status_sheet.dart — Material bottom sheet with 8 emojis, 5 presets, text input
• settings_page.dart — status section between Connection and Appearance
• members_sheet.dart — status display in channel member tiles
• app.dart — wire cache provider on auth
• nostr_models.dart — EventKind.userStatus = 30315

Test plan

• Desktop: set status from sidebar profile → verify it appears in own profile popover
• Desktop: set status → verify other users see it in their profile popover
• Desktop: clear status → verify it disappears for self and others
• Desktop: preset chips populate emoji + text correctly
• Mobile: set status from Settings → verify emoji + text appear in status tile
• Mobile: open member list in a channel → verify statuses appear as subtitles
• Mobile: clear status → verify "Set a status" placeholder returns
• Cross-platform: set status on desktop → verify it appears on mobile (and vice versa)

🤖 Generated with Claude Code

[wesbillman]