chore: move the archive-fetching tooling out of this branch

The fetching scripts and their docs now live on the `tooling` branch, which
is not published to GitHub. This removes the two references that would
otherwise dangle here: the `jd2` npm script and the CLAUDE.md bullet
describing it.

The viewer's own gallery-dl support is untouched and stays here —
src/lib/gallery-dl-sidecar.ts and friends parse sidecars at display time and
are app code, not tooling.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UXfdJu7QhSJLr47K7koTDF

package.json

@@ -12,8 +12,7 @@
     "clean": "rm -rf dist",
     "lint": "tsc --noEmit",
     "test": "vitest run",
-    "test:watch": "vitest",
-    "jd2": "tsx scripts/jd2-sync.ts"
+    "test:watch": "vitest"
   },
   "dependencies": {
     "@tailwindcss/vite": "^4.1.14",