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/biome.json

@@ -7,7 +7,15 @@
   },
   "files": {
     "ignoreUnknown": true,
-    "includes": ["**", "!node_modules", "!.next", "!dist", "!build", "!.source"]
+    "includes": [
+      "**",
+      "!node_modules",
+      "!.next",
+      "!dist",
+      "!build",
+      "!.source",
+      "!openapi.json"
+    ]
   },
   "css": {
     "parser": {