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>

sexp_effects/effects/edge_detect.sexp

@@ -0,0 +1,7 @@
+;; Edge detection effect - highlights edges
+;; @param low int [10, 100] default 50
+;; @param high int [50, 300] default 150
+
+(define-effect edge_detect
+  ((low 50) (high 150))
+  (edges frame low high))