feat(scripts): add image-to-colors + upload-colors CLI scripts

Convert PNG/JPG/WebP to rplace palette JSON (nearest-color or Floyd-Steinberg
dither) and upload at a target (x, y) with client-side credit throttling and
429 backoff. Shared palette conversion lives in src/lib/image-to-palette.js so
the browser importer can reuse it.

package-lock.json

@@ -12,6 +12,7 @@
       "devDependencies": {
         "@sveltejs/vite-plugin-svelte": "^5.0.3",
         "ioredis": "^5.10.1",
+        "sharp": "^0.34.5",
         "svelte": "^5.28.2",
         "testcontainers": "^11.14.0",
         "vite": "^6.3.2",