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/edge_detect.sexp

@@ -0,0 +1,22 @@
+;; Edge detect effect - Canny edge detection
+;; Usage: python3 plan.py effects/edge_detect.sexp -p low=50 -p high=150 | python3 execute.py - -d . -o output.mp4
+;;
+;; Parameters:
+;;   low: lower threshold (10 to 100, default: 50)
+;;   high: upper threshold (100 to 300, default: 150)
+;;         edges between low-high are kept if connected to strong edges
+
+(recipe "edge_detect"
+  :version "1.0"
+  :encoding (:codec "libx264" :crf 20 :preset "medium" :audio-codec "aac" :fps 30)
+
+  (effect edge_detect :path "sexp_effects/effects/edge_detect.sexp")
+
+  ;; Default parameters (overridden by -p low=N -p high=N)
+  (def low 50)
+  (def high 150)
+
+  (def video (source :path "monday.webm"))
+  (def clip (-> video (segment :start 0 :duration 10)))
+  (def result (-> clip (effect edge_detect :low low :high high)))
+  result)