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/sepia.sexp

@@ -0,0 +1,8 @@
+;; Sepia effect - applies sepia tone
+;; Classic warm vintage look
+
+(define-effect sepia ()
+  (color-matrix frame
+    (list (list 0.393 0.769 0.189)
+          (list 0.349 0.686 0.168)
+          (list 0.272 0.534 0.131))))