Fix type errors that failed the Docker build

- Cast the transcoder upload body to node:stream/web ReadableStream;
  the DOM ReadableStream type lacks the async-iterator members
  Readable.fromWeb expects
- Exclude transcoder/ and transcoder-remote/ from the root tsconfig:
  they are standalone sub-projects with their own tsconfig and
  dependencies (e.g. archiver) that aren't installed in the root
  node_modules, so next build's typecheck can never resolve them

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tsconfig.json

@@ -30,5 +30,5 @@
     ".next/dev/types/**/*.ts",
     "**/*.mts"
   ],
-  "exclude": ["node_modules", "public"]
+  "exclude": ["node_modules", "public", "transcoder", "transcoder-remote"]
 }