feat: paginated notification inbox API with cursor pagination and seed data

[Chucks1093]

Closes #999
Closes #1003
Closes #1006
Closes #1014

What was done

GET /api/routes-f/notifications

A new paginated notification inbox endpoint for StreamFi viewers.

Query parameters:

Param	Type	Default	Description
viewer_id	string	required	The viewer's identifier
limit	number	20	Items per page (1–100)
cursor	string	—	Notification id to start after (exclusive)

Response shape:

{
  "items": [
    {
      "id": "n_001",
      "type": "tip_received",
      "body": "CryptoKing tipped you 5 XLM during your last stream.",
      "link": "/dashboard/tips",
      "read": false,
      "created_at": "2026-06-26T10:00:00Z"
    }
  ],
  "next_cursor": "n_005",
  "unread_count": 3
}

• items — sorted newest-first; length ≤ limit
• next_cursor — the id of the last item on this page; null when no further pages exist
• unread_count — total unread notifications across all pages for this viewer (not just the current page)

Notification types supported: tip_received, new_subscriber, stream_live, clip_featured, payment_confirmed, system

Validation: missing/empty viewer_id → 400; limit outside 1–100 → 400; validated via the shared validateQuery / Zod helper

app/api/routes-f/notifications/_lib/seed.ts

In-memory seed data keyed by viewer_id:

• viewer_001 — 12 notifications (3 unread), covering all 6 notification types
• viewer_002 — 3 notifications (2 unread)
• Unknown viewers return an empty array

app/api/routes-f/notifications/__tests__/route.test.ts

17 unit tests covering:

• Input validation (missing viewer_id, empty string, limit out of range)
• Unknown viewer → empty response
• Pagination (page 1, page 2, last page, exhausted cursor)
• unread_count is the full-viewer total regardless of current page
• Newest-first ordering
• Full response shape / field type checks

[netlify]

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[github-actions]

Hi @Chucks1093 — thanks for the contribution!

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