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/fisheye.sexp

@@ -0,0 +1,20 @@
+;; Fisheye effect - barrel/pincushion distortion
+;; Usage: python3 plan.py effects/fisheye.sexp -p strength=0.5 | python3 execute.py - -d . -o output.mp4
+;;
+;; Parameters:
+;;   strength: distortion amount (-1.0 to 1.0, default: 0.5)
+;;             positive = barrel (bulge), negative = pincushion
+
+(recipe "fisheye"
+  :version "1.0"
+  :encoding (:codec "libx264" :crf 20 :preset "medium" :audio-codec "aac" :fps 30)
+
+  (effect fisheye :path "sexp_effects/effects/fisheye.sexp")
+
+  ;; Default parameter (overridden by -p strength=N)
+  (def strength 0.5)
+
+  (def video (source :path "monday.webm"))
+  (def clip (-> video (segment :start 0 :duration 10)))
+  (def result (-> clip (effect fisheye :strength strength)))
+  result)