Issue #58 — Oracle management (admin)

[GoSTEAN]

Title: [Oracle] Implement oracle address management endpoints

Tags: backend, oracle, admin, feature, security

Description:
Admin can register, update, and deactivate oracle addresses used for market resolution.

Acceptance Criteria:

• GET /oracles (admin) — lists all registered oracles with address, name, active.
• POST /oracles (admin) — registers a new oracle.
• PATCH /oracles/:id (admin) — updates name or active status.
• DELETE /oracles/:id (admin) — deactivates oracle (historical records preserved).
• DB table: oracles(id, address, name, active, created_at).

Files: src/routes/oracles.routes.ts, src/controllers/oracles.controller.ts, src/services/oracle.service.ts

---