[FEATURE] Account API Endpoints — CRUD endpoints for Stellar accounts with pagination

[gelluisaac]

Description

Implement REST endpoints for querying Stellar accounts from the database.

Endpoints

• GET /api/v1/accounts — List accounts (paginated, filterable by public_key, date range)
• GET /api/v1/accounts/{public_key} — Get single account details
• GET /api/v1/accounts/{public_key}/transactions — Transactions for a specific account
• GET /api/v1/accounts/{public_key}/fraud-summary — Fraud alerts summary for an account
• GET /api/v1/accounts/{public_key}/loyalty — Loyalty points and tier for an account

Implementation Details

• Use FastAPI dependency injection for database sessions
• Pagination via page and page_size query parameters
• Return total count for pagination metadata
• Use Pydantic schemas for request/response validation (api/schemas/)

Acceptance Criteria

• All endpoints return correct data from the database
• Pagination works correctly (default page_size=20, max=100)
• Invalid account IDs return 404
• Response format matches what the frontend expects

Labels

enhancement, api