webapi: add live SVG resource elements

[mh0pe]

Summary

• add typed gradient, stop, clip-path, mask, marker, and pattern interfaces
• implement live resource enums, transforms, percentages, defaults, and fallbacks
• use runtime-safe storage for long SVG attribute names
• centralize frame-owned animated wrapper identity across resource attributes

Stack dependency

This is unit 6 of 7. Its logical predecessor is #3031. The atomic owning commit is 9bdde1b5; GitHub targets main, so the displayed diff remains cumulative until earlier units merge.

Validation

• zig fmt --check passed
• local top-of-stack suite passed: 1,065 of 1,065 tests
• fork Zig CI passed: https://github.com/mh0pe/browser/actions/runs/30022148465
• fork plumber CI passed: https://github.com/mh0pe/browser/actions/runs/30022148395
• upstream CLA Assistant passed

Fork e2e functional jobs passed with zero failures; only cdp-and-hyperfine-bench remains queued for private lpd-bench-hetzner runner capacity.

Upstream workflow gate

Three upstream GitHub Actions suites are action_required pending maintainer approval to run fork code. This is an approval gate, not a test failure.