feat(docs): add OpenAPI API reference from oRPC contract

Generate an OpenAPI 3.1 spec from the oRPC contract at build time
using @orpc/openapi, then use fumadocs-openapi to render interactive
API reference pages grouped by tag (Titles, Episodes, Seasons, etc.).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/next.config.mjs

@@ -10,6 +10,15 @@ const config = {
     // docs site is essentially self-contained from the rest of the monorepo
     root: import.meta.dirname,
   },
+  async redirects() {
+    return [
+      {
+        source: "/docs/api",
+        destination: "/docs/api/account",
+        permanent: false,
+      },
+    ];
+  },
   async rewrites() {
     return [
       {