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.

validate-inputs/scripts/update-validators.py

@@ -311,9 +311,6 @@ class ValidationRuleGenerator:
                 "backoff-strategy": "backoff_strategy",
                 "shell": "shell_type",
             },
-            "node-setup": {
-                "package-manager": "package_manager_enum",
-            },
             "docker-publish": {
                 "registry": "registry_enum",
                 "cache-mode": "cache_mode",