Initial commit: video effects processing system

Add S-expression based video effects pipeline with modular effect
definitions, constructs, and recipe files.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

effects/contrast.py

@@ -0,0 +1,52 @@
+# /// script
+# requires-python = ">=3.10"
+# dependencies = ["numpy"]
+# ///
+"""
+@effect contrast
+@version 1.0.0
+@author artdag
+
+@description
+Adjusts contrast by scaling pixel values around the midpoint (128).
+Higher values increase contrast, lower values flatten the image.
+
+@param factor float
+  @range 0 3
+  @default 1.0
+  Contrast multiplier. 0.5 = low contrast, 1 = unchanged, 2 = high contrast.
+
+@example
+  (effect contrast :factor 1.5)
+
+@example
+  ;; Dramatic contrast on energy peaks
+  (effect contrast :factor (bind energy :range [1.0 2.0]))
+"""
+
+import numpy as np
+
+
+def process_frame(frame: np.ndarray, params: dict, state: dict) -> tuple:
+    """
+    Adjust contrast of a video frame.
+
+    Args:
+        frame: Input frame as numpy array (H, W, 3) RGB uint8
+        params: Effect parameters
+            - factor: contrast multiplier (default 1.0)
+        state: Persistent state dict (unused)
+
+    Returns:
+        Tuple of (processed_frame, new_state)
+    """
+    factor = params.get("factor", 1.0)
+
+    if factor == 1.0:
+        return frame, state
+
+    # Adjust contrast around midpoint (128)
+    img_float = frame.astype(np.float32)
+    result = 128 + factor * (img_float - 128)
+
+    return np.clip(result, 0, 255).astype(np.uint8), state