Migrate notifications to skatehive-api /api/v2/notifications endpoint

[rferrari]

Context

The API is getting a dedicated, edge-cached notifications endpoint:
SkateHive/skatehive-api#36 — GET /api/v2/notifications/[username].

It was modeled on this app's implementation (the gold standard): it returns each notification with an isRead flag (matching our HiveNotification shape), plus lastRead and an unread count, and derives read status with the same recursive last-read scan (findLastNotificationsReset logic, up to 5×1000 history ops). It supports limit (max 100) and last_id pagination.

Response:

{
  "success": true,
  "data": {
    "notifications": [{ "id": 1, "type": "reply", "score": 40, "date": "...", "msg": "...", "url": "...", "isRead": false }],
    "lastRead": "2026-07-03T03:00:00",
    "unread": 2
  }
}

Task (do this once skatehive-api#36 lands)

Switch notification reads from direct Hive RPC to the API, consistent with how lib/api.ts already consumes feed/profile/balance:

• Add a getNotifications(username, { limit, lastId }) wrapper in lib/api.ts (reuse fetchWithRetry).
• Point lib/hooks/useNotifications.ts / lib/notifications-context.tsx at the API wrapper instead of fetchAllNotifications / fetchNewNotifications in lib/hive-utils.ts.
• Map the { success, data: { notifications, lastRead, unread } } envelope to the existing HiveNotification[] shape (the isRead flag is already provided).
• Keep a direct-RPC fallback if the endpoint is unavailable (same pattern as getVideoFeed), then deprecate the RPC helpers in hive-utils.ts once stable.

Out of scope

Mark-as-read stays a client-signed broadcast (write) — the API endpoint is read-only. No change to signing.

Blocked by

• feat(api): add v2 /notifications/[username] endpoint skatehive-api#36 (endpoint)

[rferrari]

Parent tracking issue: SkateHive/skatehive-api#38.