Fix setup reliability, add Xvfb headed mode, improve inline execution

[a5m0]

Summary

• Setup script no longer depends on $CLAUDE_PROJECT_DIR — resolves skill directory from the script's own location via BASH_SOURCE[0], which always works. Also verifies the installed patchright is actually from the vendor wheel (not PyPI) and reinstalls if needed, installs trafilatura alongside patchright, and adds --system to all uv pip calls for non-venv environments.
• Headed browser mode via Xvfb — get_browser_config(headless=False) now auto-starts an Xvfb virtual display in web/CI environments. This gives better anti-bot evasion since some detection systems fingerprint headless browsers. Xvfb is installed by the setup script and also attempted at runtime as a fallback. Gracefully degrades to headless if Xvfb is unavailable.
• Simpler inline execution for common tasks — the run.py executor now auto-detects when inline code references page without creating its own browser, and provides pre-configured browser, context, page, plus all helper functions. Simple tasks become one-liners (await page.goto(...); print(await page.title())) with automatic setup and teardown.

Changes

scripts/setup-session.sh

• Resolve skill dir from script location (first priority, always works)
• Detect vendor wheel vs PyPI install and reinstall patched wheel if needed
• Install patchright + trafilatura in one pass
• Install Xvfb via apt-get (non-fatal)
• Add --system to all uv pip calls
• Fix patchright.__version__ attribute check

skills/playwright-skill/lib/proxy_wrapper.py

• Add ensure_virtual_display() / stop_virtual_display()
• Xvfb auto-install fallback at runtime via apt-get
• get_browser_config(headless=False) starts Xvfb + passes env to Chrome
• New xvfb_used key in config dict

skills/playwright-skill/run.py

• Add auto-configured inline mode (detects page. usage, provides full setup)
• Manual inline mode unchanged (detects p.chromium.launch)
• Fix multiline code indentation in all wrapper templates
• Add stop_virtual_display() cleanup to finally blocks
• Add --system to uv pip fallback installer

skills/playwright-skill/SKILL.md

• Document Xvfb headed mode and when to use it
• Document auto-configured vs manual inline execution
• Show available helpers in auto-configured mode

skills/playwright-skill/lib/helpers.py

• Export ensure_virtual_display / stop_virtual_display
• Add xvfb_used to stub get_browser_config()

Test plan

• Setup script works with empty $CLAUDE_PROJECT_DIR
• Setup script detects existing vendor wheel install
• get_browser_config() defaults to headless in web env
• get_browser_config(headless=False) starts Xvfb and Chrome connects
• Auto-configured inline: await page.goto(...) works without boilerplate
• Manual inline: p.chromium.launch(...) still works
• Complete scripts passed through unchanged
• Content extraction via extract_markdown() in auto-configured mode
• take_screenshot() in auto-configured mode
• Xvfb cleanup on exit