feat: add Sanity Studio config with hardcoded project values

The deployed Studio at hooklab.sanity.studio was crashing because it
had no access to Vercel env vars. Hardcode projectId and dataset so
sanity deploy works standalone.

https://claude.ai/code/session_01H2aRGDaKgarPvhay2HxN6Y

sanity.cli.ts

@@ -0,0 +1,8 @@
+import { defineCliConfig } from "sanity/cli";
+
+export default defineCliConfig({
+  api: {
+    projectId: "4r409ts6",
+    dataset: "production",
+  },
+});

sanity.config.ts

@@ -0,0 +1,14 @@
+import { defineConfig } from "sanity";
+import { structureTool } from "sanity/structure";
+import { portfolioSchema, siteSettingsSchema } from "./sanity/schemas";
+
+export default defineConfig({
+  name: "hooklab",
+  title: "HookLab",
+  projectId: "4r409ts6",
+  dataset: "production",
+  plugins: [structureTool()],
+  schema: {
+    types: [portfolioSchema, siteSettingsSchema],
+  },
+});