Remove prettier; we've been using biome for a while

CLAUDE.md

@@ -31,14 +31,14 @@ master process. Key design principles:
 
 ### Development
 
-**Check shell scripts (shellcheck + shfmt) (eventually go fmt and prettier or similar):**
+**Check shell scripts (shellcheck + shfmt) (eventually go fmt and biome or similar):**
 ```bash
 ./check.sh
 ```
 
 **Format TypeScript code:**
 ```bash
-cd express && ../cmd pnpm prettier --write .
+cd express && ../cmd pnpm biome check --write .
 ```
 
 **Build Go master process:**