Allow colons in jsx template tag/prop names (attr:, prop:, XML namespaces)

[brainkim]

Summary

• The jsx tagged template's parser (src/jsx-tag.ts) excluded : from its tag-name and prop-name character classes, so attr:/prop: prefixes and other XML namespace prefixes threw Unexpected text \:` even though the DOM and HTML renderers already handle them (src/dom.ts, src/html.ts`).
• Widened PROPS_RE and CHILDREN_RE to accept : in names, and added a validateName check so a leading, trailing, or repeated colon (:foo, foo:, a:b:c) is still a parse error — this is a deliberate choice, since none of those forms are meaningful namespaced names, and a loud parse error is more useful than silently accepting garbage.
• Parser-only change: renderer semantics are untouched.

All six previously-failing forms now parse to the same element shape as compiled JSX:

jsx`<div attr:foo="bar" />`
jsx`<input prop:value="x" />`
jsx`<use xlink:href="#icon" />`
jsx`<svg xmlns:xlink="http://www.w3.org/1999/xlink" />`
jsx`<svg:circle r="5" />`
jsx`<div attr:foo=${"bar"} />`

Verified colons elsewhere are unaffected: text children (<p>ratio 3:1</p>), quoted attribute values (style="color: red", href="https://x"), the <//>/<//Component> closing forms, and comments.

Test plan

• npx playwright-test test/jsx-tag.ts --runner uvu — 29/29 passed (25 baseline + 4 new tests; confirmed the count moved, since this file is excluded from npm run test:core)
• npm run test:core — 577/577 passed (unchanged from main, no regressions)
• npx tsc --noEmit — clean
• npx eslint --resolve-plugins-relative-to . src/jsx-tag.ts test/jsx-tag.ts --ext .ts,.tsx — clean
• Added a CHANGELOG entry under ## [Unreleased] (public-facing capability)
• Updated docs/guides/11-jsx-template-tag.md and docs/SKILL.md (+ regenerated skills/ via npm run skill)

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