docs(target-pkg-cdn): add comprehensive README

packages/targets/pkg-cdn/README.md

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+# @profullstack/sh1pt-target-pkg-cdn
+
+**JS/TS CDN mirror target for [sh1pt](https://sh1pt.com).**
+
+🌐 Homepage: **https://sh1pt.com**
+📦 Source: **https://github.com/profullstack/sh1pt**
+
+Validates that your npm package resolves on CDN mirrors (jsDelivr, unpkg, esm.sh, cdnjs, Skypack, JSPM) after publishing. Most CDNs auto-mirror from npm, so "shipping to CDN" really means: publish to npm first, then verify the package is reachable on each CDN.
+
+## Install
+
+```bash
+pnpm add @profullstack/sh1pt-target-pkg-cdn
+```
+
+## Configuration
+
+```ts
+interface Config {
+  /** npm package name (required) */
+  packageName: string;
+  /** CDN mirrors to check (required, at least one) */
+  mirrors: Mirror[];
+  /** cdnjs submission options (only if 'cdnjs' is in mirrors) */
+  cdnjs?: {
+    autoupdateSource: 'npm' | 'git';
+    sourceRepo?: string;
+    libraryName?: string;
+  };
+}
+
+type Mirror = 'jsdelivr' | 'unpkg' | 'esm.sh' | 'cdnjs' | 'skypack' | 'jspm';
+```
+
+## Usage
+
+### Basic: verify your package on jsDelivr + unpkg
+
+```ts
+// sh1pt.config.ts
+export default {
+  targets: {
+    'pkg-cdn': {
+      packageName: '@acme/ui',
+      mirrors: ['jsdelivr', 'unpkg'],
+    },
+  },
+};
+```
+
+### Full: all mirrors with cdnjs config
+
+```ts
+{
+  packageName: '@acme/ui',
+  mirrors: ['jsdelivr', 'unpkg', 'esm.sh', 'cdnjs', 'skypack', 'jspm'],
+  cdnjs: {
+    autoupdateSource: 'npm',
+    libraryName: 'acme-ui',
+    sourceRepo: 'https://github.com/acme/ui',
+  },
+}
+```
+
+## How it works
+
+### Build phase
+
+`sh1pt build` generates a `cdn-manifest.json` in your output directory with resolved CDN URLs for each mirror:
+
+```json
+{
+  "provider": "pkg-cdn",
+  "packageName": "@acme/ui",
+  "version": "1.2.3",
+  "mirrors": [
+    { "mirror": "jsdelivr", "url": "https://cdn.jsdelivr.net/npm/@acme/ui@1.2.3/", "source": "npm", "autoMirrored": true },
+    { "mirror": "unpkg", "url": "https://unpkg.com/@acme/ui@1.2.3/", "source": "npm", "autoMirrored": true },
+    { "mirror": "cdnjs", "url": "https://cdnjs.cloudflare.com/ajax/libs/acme-ui/1.2.3/", "source": "manual", "autoMirrored": false }
+  ]
+}
+```
+
+### Ship phase
+
+`sh1pt ship` HEAD-requests each CDN URL to verify the package resolves. If any mirror returns a non-OK status, the ship fails with a descriptive error.
+
+- **Auto-mirrored CDNs** (jsDelivr, unpkg, esm.sh, Skypack, JSPM): serve directly from npm — no extra steps after `npm publish`
+- **cdnjs**: requires a manual submission PR to the [cdnjs/packages](https://github.com/cdnjs/packages) repo
+
+## Supported CDNs
+
+| CDN | URL pattern | Auto-mirrored | Notes |
+|---|---|---|---|
+| jsDelivr | `cdn.jsdelivr.net/npm/{pkg}@{ver}/` | ✅ | Most popular, global edge network |
+| unpkg | `unpkg.com/{pkg}@{ver}/` | ✅ | Simple, reliable |
+| esm.sh | `esm.sh/{pkg}@{ver}` | ✅ | ESM-first, Deno-compatible |
+| cdnjs | `cdnjs.cloudflare.com/ajax/libs/{name}/{ver}/` | ❌ | Requires manual PR to cdnjs/packages |
+| Skypack | `cdn.skypack.dev/{pkg}@{ver}` | ✅ | Optimized for browsers |
+| JSPM | `ga.jspm.io/npm:{pkg}@{ver}/` | ✅ | Import map friendly |
+
+## Links
+
+- sh1pt: https://sh1pt.com
+- jsDelivr: https://www.jsdelivr.com
+- unpkg: https://unpkg.com
+- esm.sh: https://esm.sh
+- cdnjs: https://cdnjs.com
+- Source + issues: https://github.com/profullstack/sh1pt
+
+## License
+
+MIT