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/invert.sexp

@@ -0,0 +1,9 @@
+;; Invert effect - inverts all colors
+;; Uses vectorized invert-img primitive for fast processing
+;; amount param: 0 = no invert, 1 = full invert (threshold at 0.5)
+
+(require-primitives "color_ops")
+
+(define-effect invert
+  :params ((amount :type float :default 1 :range [0 1]))
+  (if (> amount 0.5) (color_ops:invert-img frame) frame))