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/crt.sexp

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+;; CRT effect - old TV/monitor look with scanlines and vignette
+;; Usage: python3 plan.py effects/crt.sexp -p line_spacing=3 -p vignette_amount=0.3 | python3 execute.py - -d . -o output.mp4
+;;
+;; Parameters:
+;;   line_spacing: pixels between scanlines (1 to 8, default: 3)
+;;   vignette_amount: edge darkening strength (0 to 1, default: 0.3)
+
+(recipe "crt"
+  :version "1.0"
+  :encoding (:codec "libx264" :crf 20 :preset "medium" :audio-codec "aac" :fps 30)
+
+  (effect crt :path "sexp_effects/effects/crt.sexp")
+
+  ;; Default parameters (overridden by -p line_spacing=N -p vignette_amount=N)
+  (def line_spacing 3)
+  (def vignette_amount 0.3)
+
+  (def video (source :path "monday.webm"))
+  (def clip (-> video (segment :start 0 :duration 10)))
+  (def result (-> clip (effect crt :line_spacing line_spacing :vignette_amount vignette_amount)))
+  result)