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/datamosh.sexp

@@ -0,0 +1,13 @@
+;; Datamosh effect - glitch block corruption
+;; @param block_size int [8, 128] default 32
+;; @param corruption float [0, 1] default 0.3
+;; @param max_offset int [0, 200] default 50
+;; @param color_corrupt bool default true
+
+(define-effect datamosh
+  ((block_size 32) (corruption 0.3) (max_offset 50) (color_corrupt true))
+  ;; Get previous frame from state, or use current frame if none
+  (let ((prev (state-get "prev_frame" frame)))
+    (begin
+      (state-set "prev_frame" (copy frame))
+      (datamosh frame prev block_size corruption max_offset color_corrupt))))