Add API-key scoped permission enforcement tests and documentation

[nanaf6203-bit]

Context

ApiKey model has permissions (JSON), ApiKeyAuthGuard validates keys, but key permissions aren't applied to endpoint authorization anywhere; docs/ (RBAC matrix) documents USER/AGENT/ADMIN roles, not key scopes.

Problem

API keys currently grant whatever the linked user can do - no scope limiting. An integration using a read-only key can mutate data. The permission column is stored but inert.

Proposed approach

Introduce a KeyPermissionsGuard that reads request.authUser (populated by ApiKeyAuthGuard) and enforces declared scopes against route metadata; update docs/RBAC_Permission_Matrix.md; add specs for allowed/denied scopes.

Acceptance criteria

• Scoped API keys enforce read/write limits; docs match behavior.

[samkay1277]

@samkay1277 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

I plead you to assign me to work on this issue
I have strong experience with TypeScript, NestJS, and Soroban smart contracts. I will deliver clean, tested code following the acceptance criteria.
Ready to start immediately.
Best regards,
samkay-ops

ℹ️ Repo Maintainers: To accept this application, review their application or assign @samkay1277 to this issue.

[B3N-max]

@B3N-max has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hello Maintainer
please kindly assign me this issue to fix

ℹ️ Repo Maintainers: To accept this application, review their application or assign @B3N-max to this issue.

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