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/scripts/generate-api-docs.ts

@@ -0,0 +1,9 @@
+import { generateFiles } from "fumadocs-openapi";
+import { openapi } from "../src/lib/openapi";
+
+void generateFiles({
+  input: openapi,
+  output: "./content/docs/api",
+  per: "tag",
+  addGeneratedComment: true,
+});