Incorporate art-dag-mono repo into artdag/ subfolder

Merges full history from art-dag/mono.git into the monorepo
under the artdag/ directory. Contains: core (DAG engine),
l1 (Celery rendering server), l2 (ActivityPub registry),
common (shared templates/middleware), client (CLI), test (e2e).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

git-subtree-dir: artdag
git-subtree-mainline: 1a179de547
git-subtree-split: 4c2e716558

artdag/test/sexp_effects/effects/rgb_split.sexp

@@ -0,0 +1,13 @@
+;; RGB Split effect - chromatic aberration
+
+(define-effect rgb_split
+  :params (
+    (offset_x :type int :default 10 :range [-50 50])
+    (offset_y :type int :default 0 :range [-50 50])
+  )
+  (let* ((r (channel frame 0))
+         (g (channel frame 1))
+         (b (channel frame 2))
+         (r-shifted (translate (merge-channels r r r) offset_x offset_y))
+         (b-shifted (translate (merge-channels b b b) (- offset_x) (- offset_y))))
+    (merge-channels (channel r-shifted 0) g (channel b-shifted 0))))