feat: Pretext SVG text rendering for pixel-perfect typography

[gregmeyer]

Summary

• Integrates @chenglou/pretext as an optional text rendering engine loaded via CDN into the Playwright page context
• When text_render: "pretext" is passed, headline and subheadline text is measured with Pretext's layout calculations and rendered as SVG <text> elements instead of CSS-styled HTML divs
• Default behavior (text_render: "css") is completely unchanged — this is an opt-in feature flag
• Pilot implementation on the hero layout; other layouts can adopt the pretext_slot() helper incrementally

What changed

File	Change
pretext_utils.py	New — CDN loader + DOMContentLoaded bootstrap script
pretext_renderer.py	New — pretext_slot() markup helper + svg_text_block() for static SVG
base.py	use_pretext flag + script injection in _wrap_html()
export.py	Waits for __pretextReady before Playwright screenshot
modern_hero.py	Headline + subheadline conditionally use pretext-slot
color_scheme.py	fill: currentColor rule for SVG text theme inheritance
mcp_server.py	text_render param on generate_graphic tool
rendering.py + cli.py + cli_create.py	Plumbing for the flag

Test plan

• CSS mode regression: --theme arcade hero renders identically to before
• Pretext mode: --text-render pretext --theme arcade hero renders with SVG text
• All 16 smoke tests pass
• Open HTML output in browser — Pretext bootstrap runs client-side
• Test with multiple themes (dark, warm, corporate) in pretext mode

🤖 Generated with Claude Code