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/tile_grid.sexp

@@ -0,0 +1,21 @@
+;; Tile grid effect - repeat image in grid
+;; Usage: python3 plan.py effects/tile_grid.sexp -p rows=2 -p cols=2 | python3 execute.py - -d . -o output.mp4
+;;
+;; Parameters:
+;;   rows: number of rows (1 to 8, default: 2)
+;;   cols: number of columns (1 to 8, default: 2)
+
+(recipe "tile_grid"
+  :version "1.0"
+  :encoding (:codec "libx264" :crf 20 :preset "medium" :audio-codec "aac" :fps 30)
+
+  (effect tile_grid :path "sexp_effects/effects/tile_grid.sexp")
+
+  ;; Default parameters (overridden by -p rows=N -p cols=N)
+  (def rows 2)
+  (def cols 2)
+
+  (def video (source :path "monday.webm"))
+  (def clip (-> video (segment :start 0 :duration 10)))
+  (def result (-> clip (effect tile_grid :rows rows :cols cols)))
+  result)