Doc endpoints

[LauraLangdon]

Done so far

• Added static OpenAPI 3.1.0 spec at schemas/aggregated-public-information.json
• Integrated starlight-openapi plugin into docs site — generates API reference pages at /api-reference/

##Still to do/consider:

• Review and consider styling — the default starlight-openapi rendering is functional but plain. Example of a more polished Starlight API docs site for reference: https://docs.cookie-api.com/en/docs/roblox-group-manager/endpoints/user/user-management/. As is there are also a11y contrast issues, etc. I've opened Styling is plain and not great for a11y #102 for this
• Revisit whether to add internal API docs (website, needs-assessment). See Revisit whether to add internal API docs (website, needs-assessment) #103