feat: add support for JXL, Camera RAW, ICO, TGA, PSD, EXR, HDR image formats

Extends the platform to handle 7 new image format families alongside
the existing AVIF support gap-fill. Uses the established HEIC decoder
pattern (CLI decode → PNG → Sharp) for formats Sharp can't handle
natively: Camera RAW via dcraw_emu/LibRaw, PSD/TGA/EXR/HDR via
ImageMagick. JXL and ICO are Sharp-native. Adds server-side preview
for non-browser-displayable formats and JXL as a new convert output
target. All 27 validateImageBuffer callers updated with filename for
extension-based format detection.

docker/Dockerfile.test

@@ -10,6 +10,8 @@ RUN corepack enable && corepack prepare pnpm@9.15.4 --activate
 RUN apt-get update && apt-get install -y --no-install-recommends \
     libheif-examples \
     libimage-exiftool-perl \
+    imagemagick \
+    libraw-dev \
     && if apt-cache show libheif-plugin-x265 >/dev/null 2>&1; then \
          apt-get install -y --no-install-recommends libheif-plugin-x265; \
        fi \