chore(tooling): migrate 5chan to Yarn 4

.cursor/skills/fix-merge-conflicts/SKILL.md

@@ -36,8 +36,8 @@ Open each conflicting file and remove conflict markers. Merge both sides logical
 
 | File type | Strategy |
 |-----------|----------|
-| `package.json` | Merge keys conservatively, then `yarn install` to regenerate `yarn.lock` |
-| `yarn.lock` | Never manually edit — regenerate with `yarn install` |
+| `package.json` | Merge keys conservatively, then `corepack yarn install` to regenerate `yarn.lock` |
+| `yarn.lock` | Never manually edit — regenerate with `corepack yarn install` |
 | Config files (`.json`, `.yaml`) | Preserve union of safe settings; don't delete required fields |
 | Markdown / text | Include both unique sections, deduplicate headings |
 | Binary files | Prefer current branch (ours) |
@@ -48,10 +48,10 @@ Open each conflicting file and remove conflict markers. Merge both sides logical
 Run all three checks. Fix any failures before proceeding.
 
 ```bash
-yarn build && yarn lint && yarn type-check
+corepack yarn build && corepack yarn lint && corepack yarn type-check
 ```
 
-If `package.json` was modified, run `yarn install` first.
+If `package.json` was modified, run `corepack yarn install` first.
 
 ### 4. Verify no remaining markers
 
@@ -78,6 +78,6 @@ git commit -m "chore: resolve merge conflicts"
 ## Deliverables
 
 - Clean working tree with all conflicts resolved
-- Passing `yarn build && yarn lint && yarn type-check`
+- Passing `corepack yarn build && corepack yarn lint && corepack yarn type-check`
 - One local commit: `chore: resolve merge conflicts`
 - Brief summary of files touched and notable resolution choices

.cursor/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.