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/blur.sexp

@@ -0,0 +1,20 @@
+;; Blur effect - gaussian blur
+;; Usage: python3 plan.py effects/blur.sexp -p radius=10 | python3 execute.py - -d . -o output.mp4
+;;
+;; Parameters:
+;;   radius: blur radius in pixels (1 to 50, default: 10)
+;;           higher = more blurry
+
+(recipe "blur"
+  :version "1.0"
+  :encoding (:codec "libx264" :crf 20 :preset "medium" :audio-codec "aac" :fps 30)
+
+  (effect blur :path "sexp_effects/effects/blur.sexp")
+
+  ;; Default parameter (overridden by -p radius=N)
+  (def radius 10)
+
+  (def video (source :path "monday.webm"))
+  (def clip (-> video (segment :start 0 :duration 10)))
+  (def result (-> clip (effect blur :radius radius)))
+  result)