feat(metadata): read EXIF Make tag; collect Ideogram/Recraft/Krea-FLUX

Collected live samples from three popular generators we lacked:

- Ideogram tags its downloads with EXIF Make="Ideogram AI" (no C2PA, no
  SynthID, no imwatermark) -- the Make tag is its only signal. exif_generator
  only read Software/Artist/ImageDescription, so it missed this; now reads
  Make too. Real cameras put "Apple"/"Canon" in Make (no AI token), so this
  stays low-false-positive. 4 originals ingested.
- Recraft (PNG export) and Krea hosting FLUX 2: downloads carry NO detectable
  signal -- no C2PA/EXIF/IPTC, and notably no imwatermark despite Krea running
  FLUX. identify correctly reports 'unknown'. Both ingested as neg fixtures.

Lesson recorded in CLAUDE.md: the imwatermark detector fires only on pristine
output from a pipeline that runs the encoder (diffusers default, official BFL),
not from re-hosts (Krea/Stability) or re-encoded exports (Recraft/Canva).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/remove_ai_watermarks/metadata.py

@@ -207,7 +207,15 @@ def exif_generator(image_path: Path) -> str | None:
             exif_bytes = img.info.get("exif")
         if exif_bytes:
             tags = piexif.load(exif_bytes).get("0th", {})
-            for tag in (piexif.ImageIFD.Software, piexif.ImageIFD.Artist, piexif.ImageIFD.ImageDescription):
+            # Make catches camera-style tags AI tools reuse (Ideogram writes
+            # Make="Ideogram AI"); real cameras put "Apple"/"Canon" there, which
+            # carry no AI token, so this stays low-false-positive.
+            for tag in (
+                piexif.ImageIFD.Software,
+                piexif.ImageIFD.Make,
+                piexif.ImageIFD.Artist,
+                piexif.ImageIFD.ImageDescription,
+            ):
                 value = tags.get(tag)
                 if isinstance(value, bytes):
                     candidates.append(value.decode("latin1", "replace"))