feat(visible): capture-less AI生成 pill (#54), inpaint fallback, MI-GAN backend (#56)

- Add the Jimeng-basic top-left "AI生成" pill as a CAPTURE-LESS mark
  (pill_engine.py): synthetic-silhouette edge-NCC detect + inpaint-only removal.
  Gated in remove_auto_marks: kept only when Jimeng is confirmed (TC260 metadata
  OR the bottom-right "★ 即梦AI" wordmark fired -- the wordmark keeps recall on
  metadata-STRIPPED uploads) AND Doubao did not fire.
- Add an inpaint-fallback removal path + MI-GAN ONNX backend (migan extra, MIT,
  ~28 MB / ~1 GB peak -- droplet-friendly) alongside big-LaMa. New
  --method auto|reverse-alpha|inpaint (shared across visible/all/batch) and
  erase --backend migan; footprint_mask on each engine.
- auto is deterministic: reverse-alpha for capture marks (recovers exact pixels,
  lighter -- measured cleaner than MI-GAN on structured backgrounds) and inpaint
  only for the capture-less pill.
- --mark auto now removes EVERY detected mark in one pass (remove_auto_marks),
  so a Jimeng-basic image's top-left pill AND bottom-right wordmark both clear.
- Bump 0.12.1 -> 0.13.0.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_cli.py

@@ -459,19 +459,25 @@ class TestAllCommand:
 
     def test_all_visible_step_uses_registry(self, runner, sample_png, tmp_path):
         """Regression (#1): the `all` visible step must route through the registry
-        (best_auto_mark), so Doubao/Jimeng/Samsung text marks are handled -- not just
-        the Gemini sparkle via a hardcoded GeminiEngine."""
+        (remove_auto_marks), so Doubao/Jimeng/Samsung/pill marks are handled -- not
+        just the Gemini sparkle via a hardcoded GeminiEngine."""
         mock_cls, _mock_engine = _mock_invisible_engine()
         output = tmp_path / "clean.png"
+
+        def _fake_remove_auto(image, **kwargs):
+            return image, []
+
         with (
             patch("remove_ai_watermarks.cli.InvisibleEngine", mock_cls, create=True),
             patch("remove_ai_watermarks.invisible_engine.InvisibleEngine", mock_cls),
             patch("remove_ai_watermarks.invisible_engine.is_available", return_value=True),
-            patch("remove_ai_watermarks.watermark_registry.best_auto_mark", return_value=None) as mock_best,
+            patch(
+                "remove_ai_watermarks.watermark_registry.remove_auto_marks", side_effect=_fake_remove_auto
+            ) as mock_auto,
         ):
             result = runner.invoke(main, ["all", str(sample_png), "-o", str(output), "--force"])
         assert result.exit_code == 0, result.output
-        mock_best.assert_called()  # the registry auto-detector drove the visible pass
+        mock_auto.assert_called()  # the registry auto-detector drove the visible pass
 
     def test_all_skips_invisible_on_no_signal_but_succeeds(self, runner, sample_png, tmp_path):
         """P0#5: with no detectable invisible watermark and no --force, `all` skips