Add API documentation metadata for group settlement endpoints using Fastify Swagger

[Cjay-Cyber-2]

Description — what to implement and the why/impact.

Clear API documentation improves developer experience and client SDK generation. Adding Swagger/OpenAPI metadata descriptions to group settlement routes ensures endpoints are properly documented in the generated OpenAPI schema.

Context & Requirements — background, constraints, design references, edge cases;

• Grounded in Fastify route definitions under src/routes/.
• Utilize @fastify/swagger annotations and tags consistent with existing endpoints.

Acceptance Criteria — a checklist ("- [ ] ...") of specific, testable conditions that define "done".

• Add OpenAPI schema documentation objects (summary, description, response types) to group routes.
• Verify that the Swagger UI endpoint renders the documented routes correctly without errors.

Implementation Guidance — likely files/modules to touch

• Likely files: src/routes/groups.ts or corresponding route declaration files.
• Suggested approach: Add the schema property to Fastify route options using Zod-derived JSON schemas or standard OpenAPI definitions.

Testing & Validation — how the contributor should prove it works

• Run npm run build and npm test to ensure no type or compilation errors occur.

Submission Guidelines — must open a PR that includes "Closes #"; assignment is required before starting.

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Wave complexity: Trivial

[Alanwiz00]

Hi maintainers,
I would like to work on this.

[Alanwiz00]

Hi maintainers,
I would like to work on this.

[339mon]

@339mon has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Please let me take care of this issue.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @339mon to this issue.