fix: address whole-project code review (visible all/batch, engine consolidation, I/O)

Nine findings from a high-effort project-wide review, fixed and verified
(571 passed, ruff/pyright clean):

Correctness:
- all/batch now remove Doubao/Jimeng/Samsung visible text marks: the visible
  step routes through the registry (new cli._remove_visible_auto) instead of a
  hardcoded GeminiEngine, so they no longer leave the wordmark intact.
- batch always reads the original source (dropped the out_path-reuse that
  re-processed already-cleaned outputs on a re-run).
- img2img_runner only retries the diffusion call on the deprecated-callback
  TypeError; any other TypeError now propagates instead of double-running.
- gemini detect/remove and the reverse-alpha engines normalize channels via a
  new image_io.to_bgr, fixing a grayscale/BGRA crash in the FP-gate path.
- _png_late_metadata advances its cursor by the clamped length, so a malformed
  chunk length no longer aborts the late AI-label scan.

Cleanup / efficiency:
- Consolidate the ~90%-identical Doubao/Jimeng/Samsung engines into a shared
  config-driven _text_mark_engine.TextMarkEngine base; each engine is now a thin
  subclass (TextMarkConfig + test shims). Behavior is byte-exact (the three
  engine test suites pass unchanged). Registry adapters collapse to one
  _text_mark(...) row each. Gemini stays a separate engine.
- scan_head is memoized per (path, size, mtime), so identify() reads the file
  head once instead of ~8 times.
- invisible_engine post-processing decodes/encodes the output once (chained in
  memory) instead of 2-4 times across stages.
- Remove the orphaned get_model_id_for_profile (+ CONTROLNET_PROFILE); derive
  the --strength help from the strength constants (strength_default_help) so it
  cannot drift; share the --pipeline/--strength click options; simplify the
  retired --auto resolver.

Net -835 lines. Tests added for the registry-routed visible pass, to_bgr,
the polish/model/guidance wiring, and strength_default_help. CLAUDE.md updated
for the new base module, the engine/registry changes, image_io.to_bgr, and the
scan_head cache.

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

tests/test_gemini_engine.py

@@ -124,6 +124,19 @@ class TestGeminiEngine:
         result = self.engine.remove_watermark_custom(image, (10, 10, 48, 48))
         assert result.shape == image.shape
 
+    def test_detect_on_grayscale_does_not_crash(self):
+        # A 2D grayscale array reaching detect_watermark (registry adapter / library
+        # API) must not crash the FP-gate's axis=2 reduction; it is normalized to BGR.
+        gray = np.full((300, 300), 100, dtype=np.uint8)
+        result = self.engine.detect_watermark(gray)
+        assert result is not None
+
+    def test_remove_on_bgra_returns_3_channel(self):
+        bgra = np.zeros((300, 300, 4), dtype=np.uint8)
+        bgra[..., 3] = 255
+        result = self.engine.remove_watermark(bgra)
+        assert result.shape == (300, 300, 3)
+
     def test_remove_watermark_custom_large_region(self, tmp_image_path):
         image = cv2.imread(str(tmp_image_path), cv2.IMREAD_COLOR)
         result = self.engine.remove_watermark_custom(image, (10, 10, 96, 96))