fix(types): add @cloudflare/workers-types reference to env.d.ts

Makes R2Bucket and other Cloudflare Worker globals available across
the project without per-file imports, fixing the type error in
src/lib/micro-r2.ts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: just-be-dev

src/env.d.ts

@@ -1,3 +1,5 @@
+/// <reference types="@cloudflare/workers-types" />
+
 type Runtime = import("@astrojs/cloudflare").Runtime<{
   MICRO_BUCKET: R2Bucket;
   MICRO_SECRET?: string;