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/mirror.sexp

@@ -0,0 +1,31 @@
+;; Mirror effect - mirrors half of image
+;; @param mode string default "left_right"
+
+(define-effect mirror
+  ((mode "left_right"))
+  (let* ((w (width frame))
+         (h (height frame))
+         (hw (floor (/ w 2)))
+         (hh (floor (/ h 2))))
+    (cond
+      ((= mode "left_right")
+       (let ((left (crop frame 0 0 hw h))
+             (result (copy frame)))
+         (paste result (flip-h left) hw 0)))
+
+      ((= mode "right_left")
+       (let ((right (crop frame hw 0 hw h))
+             (result (copy frame)))
+         (paste result (flip-h right) 0 0)))
+
+      ((= mode "top_bottom")
+       (let ((top (crop frame 0 0 w hh))
+             (result (copy frame)))
+         (paste result (flip-v top) 0 hh)))
+
+      ((= mode "bottom_top")
+       (let ((bottom (crop frame 0 hh w hh))
+             (result (copy frame)))
+         (paste result (flip-v bottom) 0 0)))
+
+      (else frame))))