feat(api): implement prices feature with REST endpoints for signed

[JosueBrenes]

…ice feeds

• Added PricesModule, PricesController, and PricesService to manage signed price proofs.
• Implemented endpoints to retrieve the latest prices for all symbols and for individual symbols.
• Updated README.md with new API documentation for price feeds.
• Added unit tests for PricesController and PricesService to ensure functionality.

🚀 Neko Pull Request

Mark with an x all the checkboxes that apply (like [x])

• Closes Add REST endpoints for signed price feeds (API Publisher) #32
• Added tests (if necessary)
• Run tests
• Run formatting
• Evidence attached
• Commented the code

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📌 Type of Change

• Documentation (updates to README, docs, or comments)
• Bug fix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

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📝 Changes description

Implements REST endpoints for signed price feeds (API Publisher) as described in #32.

New files:

• apps/api/src/prices/prices.module.ts — NestJS feature module for prices
• apps/api/src/prices/prices.service.ts — In-memory store for SignedPriceProof with updatePrice(), getLatestPrice(), getAllLatestPrices(), and isReady()
• apps/api/src/prices/prices.controller.ts — Two endpoints:
  • GET /prices/latest — returns all latest signed price proofs (503 if no data)
  • GET /prices/latest/:symbol — returns proof for a single symbol (404 if unknown, 503 if no data)
• apps/api/src/prices/prices.controller.spec.ts — 6 unit tests for controller
• apps/api/src/prices/prices.service.spec.ts — 8 unit tests for service

Modified files:

• apps/api/src/app.module.ts — Registered PricesModule
• apps/api/package.json — Added @oracle-stocks/signer dependency
• apps/api/README.md — Documented new routes, response shapes, and how the store is populated

No breaking changes — existing GET / and GET /health endpoints remain untouched.

Response format uses SignedPriceProof from @oracle-stocks/signer:

{
  "data": { "symbol": "AAPL", "price": 189.45, "timestamp": 1719500000000, "source": "aggregator" },
  "signature": "3045022100...",
  "publicKey": "04abc123...",
  "timestamp": 1719500000000
}

Test results: 4 suites, 23 tests passing. Build succeeds with npm run build.

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📸 Evidence (A Loom/Cap video is required as evidence, we WON'T merge if there's no proof)

(pending — will attach Loom/Cap recording)

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⏰ Time spent breakdown

Task	Time
Codebase exploration & planning	~10 min
Implementation (service, controller, module)	~15 min
Unit tests	~10 min
README documentation	~5 min
Build & test verification	~5 min
Total	~45 min

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🌌 Comments

• The PricesService uses an in-memory Map<string, SignedPriceProof> as a stub store. The updatePrice() method is exported so the aggregator/signer pipeline can push data in a future integration.
• Symbol lookup is case-insensitive (normalized to uppercase internally).
• The ingestor build failure in the pre-push hook is a pre-existing issue unrelated to these changes (as noted in the issue: "don't worry about CI workflow for now").

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