fix: HTML attributes under SKIP_TAGS subtrees never reach attr_values #104

The HTML walk in src/prose.rs (SKIP_TAGS, the !has_tag(SKIP_TAGS, tag) guard) drops whole subtrees of svg, pre, code, textarea and template. That is right for the prose stream, but the same guard also hides their attributes and <style> children from attr_values and from the StyleDoc the design group reads.

Repro (with --select design): <svg class="text-indigo-600"> and <svg><path class="fill-violet-500"/></svg> produce no violet-accent finding, while the same class on a <div> does. A <style> inside <template> is skipped too.

Fix direction: keep skipping these subtrees for text, but still collect class/style attributes and <style> bodies from them. Add an html fixture line under an <svg>.

Found reviewing PR #103.