feat(api-reference): remote OpenAPI spec + interactive API docs

[gilbertsahumada]

Summary

• Point API Reference to the OpenAPI spec hosted in ChaosChain/chaoschain (no local copy) — Mintlify fetches it on every build, so docs stay in sync automatically
• Add interactive API Reference tab with manually curated navigation groups (to exclude internal Admin endpoints)
• Add introduction page for the API Reference section with auth tiers, rate limits, and cross-links to Gateway docs
• Add cross-references between Gateway docs and API Reference (overview, public-api, workflows, verifier-context)
• Add Font Awesome icons to all navigation tabs and API Reference groups — purely cosmetic, to make the sidebar easier to scan
• Remove the reference to PUBLIC_API_SPEC.md from gateway/public-api.mdx since the interactive API Reference now serves that purpose (can be restored if preferred)

Note

The openapi URL in docs.json currently points to my fork (gilbertsahumada/chaoschain/feat/openapi-spec) so the docs can be tested before PR #40 is merged. Once #40 is merged and there are no further observations, I'll update the URL to point to ChaosChain/chaoschain/develop.

Depends on

• ChaosChain/chaoschain#40 -> Complete OpenAPI spec rewrite (must merge first so the URL points to develop)

Before merging

• PR #40 merged into develop
• Update openapi URL in docs.json from gilbertsahumada/chaoschain/feat/openapi-spec -> ChaosChain/chaoschain/develop

How it works

1. docs.json references the OpenAPI spec via raw GitHub URL -> no local openapi.yaml needed
2. Navigation groups are listed manually to control visibility (Admin endpoints excluded)
3. When the spec changes upstream, a Mintlify deploy webhook can trigger a docs rebuild (webhook setup pending)