feat(skills): hyperframes-registry skill (#261)

## What

New skill `hyperframes-registry` that teaches AI coding agents how to install and wire registry blocks and components into HyperFrames compositions.

### Skill structure
```
skills/hyperframes-registry/
  SKILL.md                          — triggers, overview, quick reference
  references/
    install-locations.md            — default paths, hyperframes.json config
    wiring-blocks.md                — iframe inclusion, data attributes, positioning
    wiring-components.md            — snippet merging (HTML, CSS, JS, timeline)
    discovery.md                    — manifest reading, item fields, available items table
    demo-html-pattern.md            — why components ship demo.html, structure conventions
  examples/
    add-block.md                    — worked example: data-chart block install + wiring
    add-component.md                — worked example: shimmer-sweep component install + wiring
```

## Why

Phase B of the catalog plan (PR 10). Without this skill, agents using `hyperframes add` have to guess how to wire installed items into compositions. The skill encodes the iframe/snippet patterns so agents get it right on the first attempt.

## How

- SKILL.md frontmatter triggers on: `hyperframes add`, "block", "component", `hyperframes.json`
- References cover every step: discovery, install, wiring blocks (iframe), wiring components (snippet merge), and the demo.html convention
- Two worked examples walk through complete install-to-preview workflows
- Updated CLAUDE.md skills table + trigger rules, README.md skills table, docs/packages/cli.mdx

## Test plan

- [x] `scripts/lint-skills.ts` passes (checked 4 skill files, no issues)
- [x] `oxfmt --check` passes on all markdown files
- [x] SKILL.md frontmatter has valid `name` and `description`
- [x] All reference links in SKILL.md resolve to existing files
- [x] CLAUDE.md, README.md, and docs CLI page updated with new skill

registry/components/grain-overlay/grain-overlay.html

@@ -68,7 +68,7 @@
     left: -50%;
     width: 200%;
     height: 200%;
-    background: url("https://www.transparenttextures.com/patterns/natural-paper.png");
+    background: url("data:image/svg+xml,%3Csvg viewBox='0 0 256 256' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noise'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.65' numOctaves='3' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noise)'/%3E%3C/svg%3E");
     opacity: 0.15;
     animation: grain-noise 0.5s steps(1) infinite;
   }