refactor: inline node-setup across Node.js actions

Phase 6A: Remove node-setup abstraction layer and inline Node.js setup.

Changes:
- Replace node-setup calls with direct actions/setup-node@v6.0.0
- Inline package manager detection (lockfile-based)
- Add Corepack enablement and package manager installation
- Use Node.js 22 as default version

Actions migrated (5):
- prettier-lint: Inline Node.js setup + package manager detection
- biome-lint: Inline Node.js setup + package manager detection
- eslint-lint: Inline Node.js setup + package manager detection
- pr-lint: Inline Node.js setup (conditional on package.json)
- npm-publish: Inline Node.js setup + package manager detection

Removed:
- node-setup/action.yml (371 lines)
- node-setup/README.md, rules.yml, CustomValidator.py
- _tests/unit/node-setup/validation.spec.sh
- _tests/integration/workflows/node-setup-test.yml
- validate-inputs/tests/test_node-setup_custom.py

Documentation updates:
- CLAUDE.md: Remove node-setup from action list (26 actions)
- generate_listing.cjs: Remove node-setup mappings
- update-validators.py: Remove node-setup custom validator

Result: 26 actions (down from 27), eliminated internal dependency layer.

pr-lint/action.yml

@@ -76,10 +76,65 @@ runs:
           printf '%s\n' "found=true" >> "$GITHUB_OUTPUT"
         fi
 
-    - name: Setup Node.js environment
+    - name: Detect Package Manager
       if: steps.detect-node.outputs.found == 'true'
-      id: node-setup
-      uses: ivuorinen/actions/node-setup@0fa9a68f07a1260b321f814202658a6089a43d42
+      id: detect-pm
+      shell: sh
+      run: |
+        set -eu
+
+        # Detect package manager from lockfiles
+        if [ -f bun.lockb ]; then
+          package_manager="bun"
+        elif [ -f pnpm-lock.yaml ]; then
+          package_manager="pnpm"
+        elif [ -f yarn.lock ]; then
+          package_manager="yarn"
+        else
+          package_manager="npm"
+        fi
+
+        printf 'package-manager=%s\n' "$package_manager" >> "$GITHUB_OUTPUT"
+        echo "Detected package manager: $package_manager"
+
+    - name: Setup Node.js
+      if: steps.detect-node.outputs.found == 'true'
+      uses: actions/setup-node@2028fbc5c25fe9cf00d9f06a71cc4710d4507903 # v6.0.0
+      with:
+        node-version: '22'
+
+    - name: Enable Corepack
+      if: steps.detect-node.outputs.found == 'true'
+      shell: sh
+      run: |
+        set -eu
+        corepack enable
+
+    - name: Install Package Manager
+      if: steps.detect-node.outputs.found == 'true'
+      shell: sh
+      env:
+        PACKAGE_MANAGER: ${{ steps.detect-pm.outputs.package-manager }}
+      run: |
+        set -eu
+
+        case "$PACKAGE_MANAGER" in
+          pnpm)
+            corepack prepare pnpm@latest --activate
+            ;;
+          yarn)
+            corepack prepare yarn@stable --activate
+            ;;
+          bun|npm)
+            # Bun installed separately, npm built-in
+            ;;
+        esac
+
+    - name: Setup Bun
+      if: steps.detect-node.outputs.found == 'true' && steps.detect-pm.outputs.package-manager == 'bun'
+      uses: oven-sh/setup-bun@735343b667d3e6f658f44d0eca948eb6282f2b76 # v2.0.2
+      with:
+        bun-version: latest
 
     - name: Cache Node Dependencies
       if: steps.detect-node.outputs.found == 'true'
@@ -87,15 +142,15 @@ runs:
       uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
       with:
         path: node_modules
-        key: ${{ runner.os }}-pr-lint-${{ steps.node-setup.outputs.package-manager }}-${{ hashFiles('package-lock.json', 'yarn.lock', 'pnpm-lock.yaml', 'bun.lockb') }}
+        key: ${{ runner.os }}-pr-lint-${{ steps.detect-pm.outputs.package-manager }}-${{ hashFiles('package-lock.json', 'yarn.lock', 'pnpm-lock.yaml', 'bun.lockb') }}
         restore-keys: |
-          ${{ runner.os }}-pr-lint-${{ steps.node-setup.outputs.package-manager }}-
+          ${{ runner.os }}-pr-lint-${{ steps.detect-pm.outputs.package-manager }}-
 
     - name: Install Node Dependencies
       if: steps.detect-node.outputs.found == 'true' && steps.node-cache.outputs.cache-hit != 'true'
       shell: sh
       env:
-        PACKAGE_MANAGER: ${{ steps.node-setup.outputs.package-manager }}
+        PACKAGE_MANAGER: ${{ steps.detect-pm.outputs.package-manager }}
       run: |
         set -eu
 

pr-lint/rules.yml

@@ -1,4 +1,3 @@
----
 # Validation rules for pr-lint action
 # Generated by update-validators.py v1.0.0 - DO NOT EDIT MANUALLY
 # Schema version: 1.0
@@ -8,7 +7,6 @@
 # Rules are automatically applied by validate-inputs action when this
 # action is used.
 #
-
 schema_version: '1.0'
 action: pr-lint
 description: Runs MegaLinter against pull requests