fix: ICO needs CLI decode, AVIF compress missing options, remove JXL output

- ICO: Sharp cannot decode ICO files. Added ImageMagick-based ICO decoder
  that extracts the largest embedded image. Added ICO to CLI_DECODED_FORMATS
  and SERVER_PREVIEW_EXTENSIONS. Removed from BROWSER_PREVIEWABLE sets.
- AVIF compress: Sharp's AVIF encoder requires effort option. Added
  formatOpts() helper that supplies effort:4 for AVIF format.
- JXL output: Docker's bundled libvips lacks the JXL encoder plugin.
  Removed JXL as a convert output target to avoid guaranteed failures.
  JXL remains fully supported as an input format.

apps/web/src/pages/tool-page.tsx

@@ -45,7 +45,6 @@ const BROWSER_PREVIEWABLE_EXTS = new Set([
   "webp",
   "svg",
   "bmp",
-  "ico",
   "avif",
 ]);