Implement Infinite Scroll Signal Feed API

[Mathews-25]

Context:
The feed must load signals quickly (<2s) and support infinite scrolling. Users should see fresh, relevant signals prioritized by quality and recency.

Problem:
Build a paginated API that returns signals efficiently with cursor-based pagination and smart filtering.

What Done Looks Like:

• GET /signals/feed with cursor pagination
• Filtering by asset, provider, performance
• Sorting by recency, popularity, success rate
• Response time under 2 seconds
• Cache frequently accessed pages

Folder Structure:

src/
├── signals/
│   ├── signals.controller.ts
│   ├── signals.service.ts
│   └── dto/
│       ├── signal-feed-query.dto.ts
│       └── signal-feed-response.dto.ts

Implementation Guidelines:

• Use cursor-based pagination (not offset/limit)
• Return 20 signals per page by default
• Include nextCursor in response for infinite scroll
• Cache feed pages in Redis (30s TTL)
• Eager load related data (provider stats, asset info)
• Apply default filter: status=ACTIVE, not expired

Query Parameters:

• cursor: string (optional, for pagination)
• limit: number (default 20, max 50)
• asset: string (e.g., "USDC/XLM")
• provider: string (wallet address)
• sortBy: "recent" | "popular" | "performance"

Response Format:

{
  "signals": [...],
  "nextCursor": "eyJpZCI6MTIzNH0=",
  "hasMore": true
}

Validation:

• First page loads under 2s
• Pagination works correctly
• Cache reduces database hits
• Filters apply correctly