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/flip.sexp

@@ -0,0 +1,14 @@
+;; Flip effect - flips image horizontally or vertically
+;; @param horizontal bool default true
+;; @param vertical bool default false
+
+(define-effect flip
+  ((horizontal true) (vertical false))
+  (let ((result frame))
+    (if horizontal
+        (set! result (flip-h result))
+        nil)
+    (if vertical
+        (set! result (flip-v result))
+        nil)
+    result))