fix(security): fix the broken admin role so /admin/* is reachable

[cypriannwokolo2-creator]

Summary

auth/service.go:149 hardcodes role: "user" in every JWT (CreateSession → GenerateJWTWithTTL(..., "user", ...)), and internal/api/middleware/auth.go:107-116 AdminMiddleware checks the JWT role claim — so no account can ever be admin, making every /admin/* endpoint unreachable via normal auth.

Acceptance Criteria

• Support admin role assignment (DB column / flag)
• Session/JWT issue correct role claim
• AdminMiddleware tests with real admin + non-admin tokens
• Admin endpoints verified reachable

Complexity

High — security + access model.

[aojomo]

@aojomo has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer, I’d like to work on this issue. Thank you

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[EmeditWeb]

@EmeditWeb has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi Maintainer, I'd love to fix this issue

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[king-daveed]

@king-daveed has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Pls assign, i can resolve

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[mayokun-max]

@mayokun-max has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

https://www.drips.network/wave/contributors/issues/881ba520-8c92-4ecb-9e51-c7530d74f820

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