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/emboss.sexp

@@ -0,0 +1,11 @@
+;; Emboss effect - creates raised/3D appearance
+;; @param strength float [0.5, 3] default 1
+;; @param blend float [0, 1] default 0.3
+
+(define-effect emboss
+  ((strength 1) (blend 0.3))
+  (let* ((kernel (list (list (- strength) (- strength) 0)
+                       (list (- strength) 1 strength)
+                       (list 0 strength strength)))
+         (embossed (convolve frame kernel)))
+    (blend-images embossed frame blend)))