Add cache config constants for public endpoints

[robertocarlous]

Closes #37

Summary
Added PUBLIC_ENDPOINT_CACHE_PRESETS (and PUBLIC_ENDPOINT_CACHE_SECONDS) in src/constants/public-endpoint-cache.constants.ts as a single shared source for public endpoint cache settings.
Updated public creators route to use the shared constants, and wired middleware CachePresets.public* to reference them (no runtime logic moved).

Testing
[x] pnpm lint
[x] pnpm build
[x] pnpm exec prisma generate

Checklist
[x] Linked issue or backlog item: #37
[x] No secrets or live credentials added
[x] Docs updated if setup or env changed (not needed)
[x] Change is scoped to one problem

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[robertocarlous]

@Chucks1093