Add slide and rotate interactive captcha solvers

New solver subsystem with independent models:
- GapDetectorCNN (1x128x256 grayscale → sigmoid) for slide gap detection
- RotationRegressor (3x128x128 RGB → sin/cos via tanh) for rotation angle prediction
- SlideSolver with 3-tier strategy: template match → edge detect → CNN fallback
- RotateSolver with ONNX sin/cos → atan2 inference
- Generators, training scripts, CLI commands, and slide track utility

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -20,6 +20,9 @@ server = [
     "uvicorn>=0.23.0",
     "python-multipart>=0.0.6",
 ]
+cv = [
+    "opencv-python>=4.8.0",
+]
 
 [project.scripts]
 captcha = "cli:main"