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/flip.sexp

@@ -0,0 +1,19 @@
+;; Flip effect - flip image horizontally or vertically
+;; Usage: python3 plan.py effects/flip.sexp -p direction=horizontal | python3 execute.py - -d . -o output.mp4
+;;
+;; Parameters:
+;;   direction: flip axis ("horizontal" or "vertical", default: "horizontal")
+
+(recipe "flip"
+  :version "1.0"
+  :encoding (:codec "libx264" :crf 20 :preset "medium" :audio-codec "aac" :fps 30)
+
+  (effect flip :path "sexp_effects/effects/flip.sexp")
+
+  ;; Default parameter (overridden by -p direction=horizontal|vertical)
+  (def direction "horizontal")
+
+  (def video (source :path "monday.webm"))
+  (def clip (-> video (segment :start 0 :duration 10)))
+  (def result (-> clip (effect flip :direction direction)))
+  result)