Generate @gonext/api-types from existing OpenAPI spec — eliminate per-page envelope adapters

[tayebmokni]

Summary

`apps/api/openapi/openapi.yaml` is the hand-authored API source of truth. The admin app and `packages/ts/sdk` each define their own decoupled `Post` / `User` / `Media` types that drift from the wire format.

Confirmed impedance mismatches between server JSON and admin TypeScript Post type alone (8+ items):

• Envelope: server `{data, pagination.next_cursor}` vs admin `{posts, nextCursor, total}`
• Author: server `author_id` vs admin `author: {id, displayName}`
• Dates: server has three (`published_at` / `updated_at` / `created_at`) vs admin's single `date`
• `commentsCount`: admin expects, server doesn't emit
• Cursor name: `pagination.next_cursor` vs `nextCursor`
• Status enum drift between admin types and server's `validStatuses`
• Nullable mismatches (server emits null timestamps, admin types as string)
• Comments package solves this differently than posts — drift between sibling modules

Per-page adapters proliferating across:

• `posts/page.tsx:121-144` — full envelope + field flattener
• `comments/types.ts:91` — `WireComment` → `Comment` translator (the GOOD pattern)
• `redirects/page.tsx:29`, `webhooks/page.tsx:37`, `jobs/dlq/page.tsx:46` — `data || []` chains
• `marketplace/actions.ts:73,113` — `body.data ?? []`

Fix

1. Add `packages/ts/api-types` workspace package.
2. Wire `openapi-typescript` to generate `packages/ts/api-types/src/index.ts` from `apps/api/openapi/openapi.yaml` on build (or commit the generated file).
3. Migrate `apps/admin` and `packages/ts/sdk` to import wire types from `@gonext/api-types`.
4. Keep UI types (`Post` with `author.displayName`) as a transformed layer, but the wire side becomes single-source.

Why P1 not P0

The current per-page adapters work. This is technical debt, not a production-down issue. But every new admin page will accumulate a copy of the same pattern until this lands.