Add invert effect with frame-by-frame API

Color inversion effect using new PEP 723 format:
- Inverts pixel values (255 - pixel)
- Intensity parameter for blending (0.0-1.0)
- Supports parameter binding to analysis data

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

invert/effect.py

@@ -0,0 +1,67 @@
+# /// script
+# requires-python = ">=3.10"
+# dependencies = ["numpy"]
+# ///
+"""
+@effect invert
+@version 1.0.0
+@author @giles@artdag.rose-ash.com
+@temporal false
+
+@description
+Inverts video colors. Each pixel value is subtracted from 255,
+creating a photographic negative effect.
+
+@param intensity float
+  @range 0.0 1.0
+  @default 1.0
+  Blend between original (0.0) and fully inverted (1.0).
+
+@example
+  (fx invert)
+
+@example
+  (fx invert :intensity 0.5)
+
+@example
+  (fx invert :intensity (bind analysis :energy :range [0.3 1.0]))
+"""
+
+import numpy as np
+
+from artdag.effects import EffectMeta, ParamSpec
+
+META = EffectMeta(
+    name="invert",
+    version="1.0.0",
+    temporal=False,
+    params=[
+        ParamSpec("intensity", float, default=1.0, range=(0.0, 1.0)),
+    ],
+)
+
+
+def process_frame(frame: np.ndarray, params: dict, state) -> tuple:
+    """
+    Invert frame colors.
+
+    Args:
+        frame: RGB frame as numpy array (H, W, 3)
+        params: {"intensity": 0.0-1.0}
+        state: Unused, passed through
+
+    Returns:
+        (inverted_frame, state)
+    """
+    intensity = params.get("intensity", 1.0)
+
+    # Invert: 255 - pixel
+    inverted = 255 - frame
+
+    # Blend based on intensity
+    if intensity < 1.0:
+        result = (frame * (1 - intensity) + inverted * intensity).astype(np.uint8)
+    else:
+        result = inverted.astype(np.uint8)
+
+    return result, state