chore(tooling): migrate 5chan to Yarn 4

.codex/skills/readme/SKILL.md

@@ -154,7 +154,7 @@ bundle install
 ### 3. Install JavaScript Dependencies
 
 \`\`\`bash
-yarn install
+corepack yarn install
 \`\`\`
 
 ### 4. Environment Setup
@@ -708,7 +708,7 @@ The master key doesn't match the credentials file. Either:
 rm -rf node_modules/.vite
 
 # Reinstall JS dependencies
-rm -rf node_modules && yarn install
+rm -rf node_modules && corepack yarn install
 \`\`\`
 
 ### Solid Queue Issues
@@ -761,4 +761,4 @@ Generate a complete README.md file with:
 - Clear section hierarchy
 - Linked table of contents for long documents
 
-Write the README directly to `README.md` in the project root.
+Write the README directly to `README.md` in the project root.