Add deep detection via jsdom and URL scanning via Puppeteer

Three detection tiers:
- file/dir (default): fast regex scan, zero dependencies
- file + --deep: jsdom computed styles, resolves linked local stylesheets
  by inlining <link rel="stylesheet"> content before parsing
- URL (https://...): auto-launches Puppeteer for full browser rendering,
  handles CDN stylesheets, JS-rendered content, everything

New exports: detectAntiPatternsDeep(), detectAntiPatternsUrl()
jsdom added as devDependency; puppeteer remains optional (npx cache).

TDD: linked-stylesheet fixture demonstrates the gap — regex finds 0
border issues, --deep correctly catches side-tab and top-accent from
the external CSS file.

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

package.json

@@ -31,6 +31,7 @@
   },
   "type": "module",
   "devDependencies": {
+    "jsdom": "^29.0.0",
     "wrangler": "^4.71.0"
   }
 }