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/sharpen.sexp

@@ -0,0 +1,9 @@
+;; Sharpen effect - sharpens edges
+;; @param amount float [0, 5] default 1
+
+(define-effect sharpen
+  ((amount 1))
+  (let ((kernel (list (list 0 (- amount) 0)
+                      (list (- amount) (+ 1 (* 4 amount)) (- amount))
+                      (list 0 (- amount) 0))))
+    (convolve frame kernel)))