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/trails.sexp

@@ -0,0 +1,20 @@
+;; Trails effect - motion blur/persistence
+;; Usage: python3 plan.py effects/trails.sexp -p persistence=0.7 | python3 execute.py - -d . -o output.mp4
+;;
+;; Parameters:
+;;   persistence: trail strength (0.3 to 0.95, default: 0.7)
+;;                higher = longer trails
+
+(recipe "trails"
+  :version "1.0"
+  :encoding (:codec "libx264" :crf 20 :preset "medium" :audio-codec "aac" :fps 30)
+
+  (effect trails :path "sexp_effects/effects/trails.sexp")
+
+  ;; Default parameter (overridden by -p persistence=N)
+  (def persistence 0.7)
+
+  (def video (source :path "monday.webm"))
+  (def clip (-> video (segment :start 0 :duration 10)))
+  (def result (-> clip (effect trails :persistence persistence)))
+  result)