feat(registry): seed transition blocks — 14 shader + 14 CSS showcase (#270)

## What

Add 28 transition blocks from the Hyperframe Template Structure catalog, bringing the registry to 53 total items.

### Shader transitions (14 blocks, WebGL, 4s each)
`domain-warp-dissolve`, `ridged-burn`, `whip-pan`, `sdf-iris`, `ripple-waves`, `gravitational-lens`, `cinematic-zoom`, `chromatic-radial-split`, `glitch`, `swirl-vortex`, `thermal-distortion`, `flash-through-white`, `cross-warp-morph`, `light-leak`

### CSS transition showcases (14 blocks, various durations)
`transitions-3d`, `transitions-blur`, `transitions-cover`, `transitions-destruction`, `transitions-dissolve`, `transitions-distortion`, `transitions-grid`, `transitions-light`, `transitions-mechanical`, `transitions-other`, `transitions-push`, `transitions-radial`, `transitions-scale`, `transitions-shader`

## Why

Phase D content accumulation. Transitions are the most-requested category for the catalog.

## How

- Shader transitions extracted from `shader-showcase.zip`, each a standalone HTML with WebGL shaders
- CSS transitions extracted from `showcase-bundle.zip`, each a standalone showcase page
- All tagged with `transition` + `shader` or `showcase` for catalog grouping
- Preview thumbnails generated for all 28 blocks
- Catalog pages + index regenerated

## Test plan

- [x] All 28 blocks produce preview thumbnails
- [x] `registry-item.json` validates for all blocks
- [x] Catalog pages generated (45 total items in catalog-index.json)
- [x] `oxfmt --check` passes

docs/catalog/blocks/cinematic-zoom.mdx

@@ -0,0 +1,44 @@
+---
+title: "Cinematic Zoom"
+description: "Shader transition with dramatic zoom blur"
+---
+
+# Cinematic Zoom
+
+Shader transition with dramatic zoom blur
+
+`transition` `shader`
+
+<video className="w-full aspect-video rounded-xl object-cover bg-zinc-100 dark:bg-zinc-800" src="/images/catalog/blocks/cinematic-zoom.mp4" poster="/images/catalog/blocks/cinematic-zoom.png" autoPlay muted loop playsInline />
+
+## Install
+
+<CodeGroup>
+
+```bash Terminal
+npx hyperframes add cinematic-zoom
+```
+
+</CodeGroup>
+
+## Details
+
+| Property | Value |
+| --- | --- |
+| Type | Block |
+| Dimensions | 1920×1080 |
+| Duration | 4s |
+
+## Files
+
+| File | Target | Type |
+| --- | --- | --- |
+| `cinematic-zoom.html` | `compositions/cinematic-zoom.html` | hyperframes:composition |
+
+## Usage
+
+After installing, add the block to your host composition:
+
+```html
+<div data-composition-id="cinematic-zoom" data-composition-src="compositions/cinematic-zoom.html" data-start="0" data-duration="4" data-track-index="1" data-width="1920" data-height="1080"></div>
+```