fix(visible): guard extract_mask against degenerate ROIs (Windows CI crash)

The always-align removal scores each placement with a residual detect(),
which on an extremely wide/short image (2048x1, test_wide_short_does_not_raise)
fed cv2 GaussianBlur a ~1-px-tall ROI and faulted natively on Windows py3.12
(access violation, non-deterministic -- one CI cell went red, a re-run passed).
The old at-native path never ran detect() on degenerate sizes. Skip the cv2
pipeline and return an empty mask when bh < 16 or bw < 16; real images always
clear the guard (the WM_* box floors are max(16,..) / max(40,..)). Same fix in
both Doubao and Jimeng. Also sync the stale Doubao module docstring.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/remove_ai_watermarks/jimeng_engine.py

@@ -238,6 +238,13 @@ class JimengEngine:
         """
         h, w = image.shape[:2]
         x, y, bw, bh = loc.bbox
+        # A degenerate ROI (a sliver from an extremely wide/short image) cannot hold
+        # the mark and would feed cv2's GaussianBlur/morphology a ~1-px-tall array,
+        # which can fault the native code on some platforms (observed: a Windows
+        # access violation via the always-align removal's residual `detect`). Skip
+        # the cv2 pipeline and return an empty mask there.
+        if bh < 16 or bw < 16:
+            return np.zeros((h, w), np.uint8)
         # Normalize the ROI to 3-channel BGR: a 2D grayscale or 4-channel BGRA
         # input would otherwise break the axis=2 channel reductions below.
         roi = image[y : y + bh, x : x + bw]