feat(registry): seed blocks batch — social overlays, data viz, showcases (#269)

## What

Add 11 blocks from the Hyperframe Template Structure catalog, bringing the registry to 25 total items.

### Social overlays
| Block | Dimensions | Duration | Description |
|-------|-----------|----------|-------------|
| `instagram-follow` | 1080×1920 | 4.5s | Instagram follow overlay with profile card |
| `tiktok-follow` | 1080×1920 | 4.5s | TikTok follow overlay with profile card |
| `yt-lower-third` | 1920×1080 | 4.5s | YouTube subscribe lower third |
| `x-post` | 1920×1080 | 5s | X/Twitter post card with engagement |
| `reddit-post` | 1920×1080 | 5s | Reddit post card with upvotes |
| `spotify-card` | 1080×1920 | 5s | Spotify now-playing card |
| `macos-notification` | 1920×1080 | 5s | macOS notification banner |

### Data & visualization
| Block | Duration | Description |
|-------|----------|-------------|
| `ascii-dashboard` | 10s | Retro terminal-style data viz |
| `ascii-lightning` | 9s | ASCII art lightning bolt animation |

### Showcases
| Block | Duration | Description |
|-------|----------|-------------|
| `app-showcase` | 5.5s | Floating smartphone screens |
| `ui-3d-reveal` | 13s | Perspective 3D UI reveal |

## Why

Phase D content accumulation. The registry pipeline (PRs 6-10) is in place — this PR exercises it at scale.

## How

- Extracted from zip files in the Hyperframe Template Structure Notion doc
- Social overlays: single-file standalone HTML, copied directly
- Multi-file blocks (ascii-*, app-showcase, ui-3d-reveal): converted `<template>` sub-compositions to standalone HTML with proper `<!doctype>` wrappers
- All previews (PNG + MP4) rendered locally via `generate-catalog-previews.ts`
- Catalog MDX pages regenerated via `generate-catalog-pages.ts`
- `docs.json` updated with new catalog entries

## Test plan

- [x] All 11 blocks render to PNG + MP4 without errors
- [x] Catalog pages generated for all 17 items (14 blocks + 3 components)
- [x] `registry-item.json` files have correct dimensions, duration, tags
- [x] `oxfmt --check` passes on all files

docs/catalog/blocks/tiktok-follow.mdx

@@ -0,0 +1,45 @@
+---
+title: "TikTok Follow"
+description: "Animated TikTok follow overlay with profile card and follow button"
+---
+
+# TikTok Follow
+
+Animated TikTok follow overlay with profile card and follow button
+
+`social` `overlay` `tiktok`
+
+<video className="w-full aspect-video rounded-xl object-cover bg-zinc-100 dark:bg-zinc-800" src="/images/catalog/blocks/tiktok-follow.mp4" poster="/images/catalog/blocks/tiktok-follow.png" muted loop playsInline autoPlay />
+
+## Install
+
+<CodeGroup>
+
+```bash Terminal
+npx hyperframes add tiktok-follow
+```
+
+</CodeGroup>
+
+## Details
+
+| Property | Value |
+| --- | --- |
+| Type | Block |
+| Dimensions | 1080×1920 |
+| Duration | 4.5s |
+
+## Files
+
+| File | Target | Type |
+| --- | --- | --- |
+| `tiktok-follow.html` | `compositions/tiktok-follow.html` | hyperframes:composition |
+| `assets/avatar.jpg` | `assets/avatar.jpg` | hyperframes:asset |
+
+## Usage
+
+After installing, add the block to your host composition:
+
+```html
+<div data-composition-id="tiktok-follow" data-composition-src="compositions/tiktok-follow.html" data-start="0" data-duration="4.5" data-track-index="1" data-width="1080" data-height="1920"></div>
+```