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/hue_shift.sexp

@@ -0,0 +1,20 @@
+;; Hue shift effect - rotate colors around color wheel
+;; Usage: python3 plan.py effects/hue_shift.sexp -p degrees=90 | python3 execute.py - -d . -o output.mp4
+;;
+;; Parameters:
+;;   degrees: hue rotation in degrees (0 to 360, default: 90)
+;;            90 = quarter rotation, 180 = complementary colors
+
+(recipe "hue_shift"
+  :version "1.0"
+  :encoding (:codec "libx264" :crf 20 :preset "medium" :audio-codec "aac" :fps 30)
+
+  (effect hue_shift :path "sexp_effects/effects/hue_shift.sexp")
+
+  ;; Default parameter (overridden by -p degrees=N)
+  (def degrees 90)
+
+  (def video (source :path "monday.webm"))
+  (def clip (-> video (segment :start 0 :duration 10)))
+  (def result (-> clip (effect hue_shift :degrees degrees)))
+  result)