Docs: Add OpenAPI specs for list, distribute, history, update_collabo…

[iGEORGE17]

📝 Description
This PR addresses issue #104 by documenting the missing endpoints required for full interaction with the SplitNaira smart contracts and backend. These additions ensure that the frontend and external integrators have a clear contract for listing splits, triggering distributions, viewing history, and managing collaborators.

🚀 Scope of Changes
New Endpoints Added:

GET /splits: Added pagination and status filtering.

POST /splits/{id}/distribute: Documented the trigger for fund dispersal.

GET /splits/{id}/history: Added audit trail for split lifecycle events.

PUT /splits/{id}/collaborators: Defined schema for updating participant addresses and share ratios.

Schema Enhancements:

Updated BuildTransactionMetadata examples to include varied contexts (distribution vs. collaborator updates).

Standardized error responses (404 for missing splits, 400 for invalid share totals).

✅ Acceptance Criteria Check
[x] OpenAPI file passes spectral linting with zero errors.

[x] All new endpoints render correctly in Swagger UI.

[x] Request/Response examples provided for all new paths.

📸 Documentation Preview
[!TIP]
You can view the rendered version of these changes by pasting the openapi.yaml content into the Swagger Editor.

🧪 How to Test
Pull this branch: git checkout docs-update-104.

Run the local docs server: npm run docs:dev (or your equivalent command).

Navigate to /docs or the Swagger UI endpoint.

Verify that the distribute and collaborators endpoints correctly display the BuildTransactionMetadata object in the response example.

Closes #104

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