fix(api): decode RAW via LibRaw first so DNG processes at full resolution (#289) (#290)

RAW (DNG) processing crashed on ImageMagick's deprecated ufraw-batch
delegate, which fails on modern formats such as iPhone ProRAW DNG.

Root cause: the dcraw_emu (LibRaw) decode tier read the wrong output path.
dcraw_emu APPENDS the output extension (raw-in-X.dng -> raw-in-X.dng.tiff)
but the code looked for raw-in-X.tiff (replaced extension), so readFile threw
on every RAW, the tier silently fell through to ufraw, and the 24MB TIFF
leaked into the temp dir on each attempt.

- Repair the dcraw_emu output path; clean it up in finally (fixes the leak)
- Prefer LibRaw full decode over embedded-preview extraction so a
  full-resolution RAW is never silently returned as a reduced-size preview
  (sample DNG: was 1024x683 preview, now 3474x2314 full)
- Add RAW decode regression tests (DNG full-resolution + all 6 RAW formats);
  these were absent, which let the bug ship
- Install libraw-bin on CI test runners so dcraw_emu is actually exercised

.github/workflows/nightly.yml

@@ -9,7 +9,7 @@ permissions:
   contents: read
 
 env:
-  SYSTEM_DEPS: libheif-examples libheif-plugin-x265 libheif-plugin-libde265 libimage-exiftool-perl imagemagick ghostscript libjxl-tools libopenjp2-tools ffmpeg qpdf
+  SYSTEM_DEPS: libheif-examples libheif-plugin-x265 libheif-plugin-libde265 libimage-exiftool-perl libraw-bin imagemagick ghostscript libjxl-tools libopenjp2-tools ffmpeg qpdf
 
 jobs:
   e2e-full: