feat: real-time live activity feed for platform-wide registrations & claims

[springswell]

Summary

Adds a real-time, platform-wide live activity feed: a ticker of recent campaign registrations and reward claims, pushed over the existing WebSocket server (#456) instead of polled.

How it works

on-chain event ─▶ eventIndexer (claim / register projected)
                   └─ onActivity(...) ─▶ WebSocketServer.publishActivity()
                                          └─ broadcast to room "activity" ─▶ <LiveActivityFeed />

Backend

• backend/src/jobs/eventIndexer.js:
  • New optional onActivity callback on createEventIndexer.
  • The claim and register handlers call it through emitActivity() after the event has been projected into the DB.
  • Errors from the callback are caught and logged, so the feed can never stall indexing.
  • When no callback is passed, the indexer behaves as before.
• backend/src/websocket/server.js:
  • New publishActivity(activity) broadcasts { type: 'activity', id, kind, wallet, campaignId, amount, ledger, timestamp } to the new activity room.
  • Only the registration and claim kinds are accepted.
  • Privacy: wallets are masked server-side as GABC…WXYZ via maskWallet. The message id uses only kind:txHash, so the full address never reaches subscribers.
• backend/src/index.js: passes onActivity to the indexer. It resolves getWebSocketServer() lazily, because the WS server is attached after the HTTP server starts listening. When WebSockets are disabled, nothing is sent.

Clients opt in with the existing subscribe protocol, { type: 'subscribe', channel: 'activity' }, so there's no protocol change.

Frontend

• frontend/src/lib/activityFeed.js: pure helpers:
  • normalizeActivity rejects malformed frames defensively;
  • addActivity puts newest first, de-duplicates by id and caps at 20;
  • formatActivityAmount converts stroops to points;
  • describeActivity and formatRelativeTime build the display text.
• frontend/src/components/LiveActivityFeed.jsx:
  • Uses the existing getWebSocketClient() singleton, whose reconnect/resubscribe logic already existed.
  • Subscribes to activity and shows a Live / Connecting… status indicator.
  • Relative times refresh every 15s.
  • Uses an aria-live list and unsubscribes on unmount.
  • The client can be injected via the client prop for tests or Storybook.
• frontend/src/components/LiveActivityFeed.css: slide-in and pulse micro-animations, disabled under prefers-reduced-motion. Uses theme tokens with fallbacks, so it follows light and dark themes.

Tests

backend/src/websocket/activity-feed.test.js (node:test) covers:

• maskWallet;
• emitActivity mapping for claims and registrations, a missing wallet, a missing callback and a throwing callback;
• an end-to-end subscribe → publishActivity → receive test, which also asserts the full wallet never appears in the payload;
• rejection of unknown kinds.

Not done / not verified (raised early on request)

• The tests weren't confirmed passing. Backend deps were installed, but the run hadn't finished when this PR was opened. No frontend unit tests were added for activityFeed.js or the component yet.
• The widget isn't mounted on a page yet. <LiveActivityFeed /> is exported and ready to drop into Landing.jsx or a dashboard; I left the placement to maintainers.
• Replaying pending events after a reorg or confirmation delay may re-emit an item. The frontend de-duplicates by kind:txHash, which covers this.
• Mainnet/testnet end-to-end runs weren't done.
  Closes feat(frontend): Real-time live activity feed widget for platform-wide claims #1201
  Closes feat(frontend): Dark and Light mode theme switcher with system preference detection #1202
  Closes feat(frontend): Add Global Command Palette (⌘K / Ctrl+K) for rapid navigation #1205
  Closes feat(frontend): Campaign Leaderboard component with seasonal filter and rank badges #1206

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