feat: add Playwright screenshot generation for wp-admin pages

[mpge]

Summary

• Adds a GitHub Actions workflow that spins up WordPress with a MySQL service container, installs/activates the Escalated plugin, and uses Playwright to capture screenshots of all 11 wp-admin pages (Ticket List, Ticket Detail, Departments, SLA Policies, Automations, Tags, Canned Responses, Macros, Reports, Settings, API Tokens).
• Triggers on version tags (v*) and manual workflow_dispatch; screenshots are uploaded as build artifacts and optionally committed back to main on tag pushes.
• Includes Playwright config, test spec, .gitignore for node_modules/ and vendor/, and a .gitkeep to track the results directory.

Test plan

• Trigger the workflow manually via Actions > "Generate Screenshots" > Run workflow
• Verify all 11 screenshot PNGs appear in the escalated-wp-screenshots artifact
• Confirm the workflow completes without errors on a fresh run
• Test tag-triggered run to verify screenshots are committed back to main