fix(invisible): ctrlregen defaults to clean-noise strength, not the SDXL 0.10

The ctrlregen profile inherited the SDXL img2img --strength default (0.10), a
near-identity pass that loaded ControlNet + DINOv2-giant and barely changed the
image -- a no-op for removal. resolve_strength() now resolves an unset strength
per profile: 0.10 for the SDXL default, CTRLREGEN_DEFAULT_STRENGTH (1.0,
clean-noise) for ctrlregen. It checks `is None` rather than falsiness, so an
explicit 0.0 is respected (the old `strength or DEFAULT` swallowed it).

Research basis: CtrlRegen (ICLR 2025, arXiv:2410.05470) removes robust
watermarks by regenerating from clean Gaussian noise; partial-noise img2img
retains watermark info that diffuses back, so a high (clean-noise) strength is
the lever, not a knob on the light SDXL pass. CLI wiring (--strength default
None) lands with the cli refactor.

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

src/remove_ai_watermarks/invisible_engine.py

@@ -19,8 +19,6 @@ import warnings
 from pathlib import Path
 from typing import TYPE_CHECKING
 
-from remove_ai_watermarks.noai.watermark_profiles import DEFAULT_STRENGTH
-
 if TYPE_CHECKING:
     from collections.abc import Callable
 
@@ -135,7 +133,8 @@ class InvisibleEngine:
         Args:
             image_path: Path to the watermarked image.
             output_path: Output path (None = overwrite source).
-            strength: Denoising strength (0.0-1.0). None -> DEFAULT_STRENGTH (0.10).
+            strength: Denoising strength (0.0-1.0). None -> profile default
+                (0.10 for SDXL, 1.0 clean-noise for ctrlregen).
             steps: Number of denoising steps.
             guidance_scale: Classifier-free guidance scale.
             seed: Random seed for reproducibility.
@@ -281,7 +280,7 @@ class InvisibleEngine:
         self,
         input_dir: Path,
         output_dir: Path,
-        strength: float = DEFAULT_STRENGTH,
+        strength: float | None = None,
         steps: int = 50,
     ) -> list[Path]:
         """Remove invisible watermarks from all images in a directory."""