feat(backend): Implement API key management for programmatic access

[KuchiMercy]

Description

api-key module exists with files. Complete implementation: scoped API key generation, rotation, revocation, and usage tracking.

Module: src/api-key/

Acceptance Criteria

• ApiKey entity: id, userId, name, keyHash, keyPrefix (vlt_...), scopes, isActive, lastUsedAt, expiresAt
• POST /api-keys — generate key with name, scopes, optional expiration
• Return full key only once at creation
• Scopes: read:escrows, write:escrows, read:analytics, admin
• GET /api-keys (list with prefix only)
• PATCH /api-keys/:id (update name/scopes/status)
• DELETE /api-keys/:id (revoke)
• POST /api-keys/:id/rotate (new key, deactivate old)
• ApiKeyGuard middleware for X-API-Key header
• Coexists with JWT auth
• Bcrypt hashed storage
• Async lastUsedAt tracking
• Separate rate limiting (200 req/min)
• Max 5 active keys per user
• Auto-deactivate expired keys
• Unit and E2E tests

Points: 150

[Properprogress1]

@Properprogress1 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Please assign me this task, ETA is 5hrs

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[drips-wave]

Congratulations, @Properprogress1! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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