Add BDD + PageObject skills and @bdd-copilot agent

[miroslavpojer]

Summary

Adds 6 BDD and PageObject skills and the @bdd-copilot agent — the automation layer
for web app exploration, scenario generation, and BDD maintenance.

Depends on Issue 1a: living-doc-gap-finder and @living-doc-copilot must already
be in the repo.

Skills

• living-doc-pageobject-scan
• living-doc-scenario-creator
• living-doc-tutorial-creator
• gherkin-scenario
• gherkin-step
• gherkin-living-doc-sync

Note: living-doc-gap-finder ships in Issue 1a — this PR only references it.

Agent

.github/agents/bdd-copilot.agent.md