feat: add SVG output format support

[jackspirou]

Add support for generating animated SVG files as an output format.

• Add new SVG generator with CSS keyframe animations
• Support all existing VHS style options (margins, padding, themes, etc.)
• Add frame deduplication for optimized file sizes
• Update documentation and examples to include SVG format
• Add test coverage for SVG generation

[jackspirou]

Closing in favor of a new PR with improved implementation and comprehensive test coverage.

[jackspirou]

The SVG benefit audit now includes this original proposal. Native SVG output, CSS playback, frame reuse, tape/CLI/SSH output paths, documentation, examples, and generation tests remain in the later implementation.

The audit found two style gaps in current main: SVG ignored authored cursor colors, and captured rows had LineHeight applied twice. PR #14 is now merged at eeb09ba. It restores cursor colors with the existing fallbacks, uses captured row spacing once, and corrects the optimization example. These are implemented repairs, not closure-only resolutions.

Native Chrome capture and pixel regressions pass. The full native race suite passes 303 cases with no failed or skipped tests. Root verification passes 24 focused cases. All eight hosted checks, pre-PR autoreview, and the exact-content secret scan passed.

Thank you for the original SVG proposal and its style, size, documentation, and test requirements. The audit tracks those benefits through the replacement implementation and the current repairs.