Self-hosted Studio: Auth → Sign In / Providers stuck on skeleton loaders (IS_PLATFORM + static export / platform auth API parity)

### Summary On **self-hosted** Supabase Studio, **Authentication → Sign In / Providers** (`/project/:ref/auth/providers`) can stay on **infinite skeleton loaders** indefinitely. The UI never receives auth configuration data, so "User Signups", provider toggles, etc. never render. This is a **self-hosted / Studio packaging** issue, not an end-user misconfiguration. ### What we observed (technical) 1. **`IS_PLATFORM` gating** Auth config is loaded via a hook aligned with the cloud product (`useAuthConfigQuery` / `authKeys.authConfig`). In shipped bundles the query’s `enabled` predicate can include `… && IS_PLATFORM && …`. On self-hosted, `NEXT_PUBLIC_IS_PLATFORM` is **`false`**, so the query **never runs** and TanStack Query v5 stays pending → skeletons forever. 2. **Static export / empty `router.query`** Studio is effectively served as static assets; on first paint **`router.query` may be empty**, so `projectRef` from `useParams()` is **undefined**. Some layouts also normalize with a **`"_"` placeholder**, which then produces requests like `GET …/platform/auth/_/config` instead of the real project ref. 3. **Platform API parity** Cloud Studio calls **`GET /api/platform/auth/:ref/config`**. A typical self-hosted ingress stack (e.g. Kong + Studio) **does not implement** that route; if the request falls through to the Studio SPA, the client gets **HTML** instead of JSON, which also breaks the page. ### Related upstream (similar class of bug) - #36285 — self-hosted **Edge Functions** home stuck on skeleton loaders (same “never finishes loading” symptom). - #33557 — intentional **`IS_PLATFORM`** checks for local/self-hosted; the pattern is easy to apply in ways that **disable** queries that are still required for core Auth UI. ### Suggested direction for a proper fix 1. **Auth settings reads** that power the Sign In / Providers page should have a **first-class self-hosted path**: either - relax `enabled` when `projectRef` can be derived from the URL (`/…