Bump skills to 3.0, remove prefixed bundle, redesign install section

- Bump skills plugin version 2.1.1 -> 3.0.0 (plugin.json, marketplace.json,
  harness SKILL.md files). CLI and Chrome extension unchanged.
- Remove prefixed universal zip bundle and all related code:
  factory.js prefix/outputSuffix options, zip.js variant pass, utils.js
  prefixSkillReferences, the "universal-prefixed" entry in
  download-providers.js, and the matching test suite in utils.test.js.
- Redesign Get Started step 1 "Install the skill and CLI": two terminal
  rows (npx skills + npm i -g impeccable) with paired notes, drop the
  Recommended badge.
- Collapse "Other install methods" back into a <details> element so the
  primary install path is the first thing users see.
- Simplify step 3 to "Add the Chrome extension": remove the CLI tool
  block (now in step 1), use standard .btn .btn-primary for the CTA so
  it matches other primary buttons (square corners, accent slide-up
  hover), and lay out the preview screenshot next to the button instead
  of stacked so the screenshot no longer dominates vertical space.
- CLAUDE.md: rewrite with v3.0 architecture, the "no em dash also means
  no --" rule, the harness-dirs-are-tracked gotcha, the named-export
  test-spy warning, and the evals inline-skill.ts sync note.
- AGENTS.md, DEVELOP.md: drop prefixed variant references.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.opencode/skills/impeccable/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: impeccable
 description: "Design fluency for frontend interfaces. Build distinctive, production-grade web components, pages, artifacts, posters, and applications with high design quality. Also handles: critique/review/evaluate designs, audit accessibility/performance/responsive, polish finishing touches, improve typography/fonts/readability, fix layout/spacing/hierarchy, add animation/transitions/motion, adapt for mobile/tablet/responsive, simplify/declutter/distill, amplify bland/generic/safe designs, tone down loud/overwhelming designs, add color to gray/monochromatic interfaces, improve UX copy/labels/error messages, harden for production with edge cases/i18n/errors/empty states, optimize slow/laggy performance, plan UX before coding, extract design tokens, or push boundaries with shaders/physics/scroll effects. Commands: craft, teach, extract, pin, audit, critique, polish, shape, adapt, animate, bolder, quieter, colorize, clarify, delight, distill, harden, layout, optimize, overdrive, typeset."
-version: 2.1.1
+version: 3.0.0
 user-invocable: true
 argument-hint: "[command] [target]"
 license: Apache 2.0. Based on Anthropic's frontend-design skill. See NOTICE.md for attribution.