Wire admin authentication middleware into admin routes

[hman38705]

Issue 001: Wire admin authentication middleware into admin routes

Area: Backend
Priority: Critical
Files: services/api/src/main.rs, services/api/src/security.rs

Problem

Admin routes are labeled as protected but no API key middleware is attached. Any caller can access admin endpoints without authentication.

Acceptance Criteria

• x-api-key header is required for all admin endpoints\n- Invalid or missing key returns 401 Unauthorized\n- Tests cover authorized and unauthorized calls\n- Middleware is applied before route handlers execute

[Macnelson9]

@Macnelson9 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hi, can I work on this issue please? I will deliver timely and efficiently. ETA: 1hr

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Congratulations, @Macnelson9! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @Macnelson9: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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This issue has been completed by @Macnelson9 as part of the Stellar Wave Program's 4th Wave 🥳

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