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/bloom.sexp

@@ -0,0 +1,16 @@
+;; Bloom effect - glow on bright areas
+(require-primitives "image" "blending")
+
+(define-effect bloom
+  :params (
+    (intensity :type float :default 0.5 :range [0 2])
+    (threshold :type int :default 200 :range [0 255])
+    (radius :type int :default 15 :range [1 50])
+  )
+  (let* ((bright (map-pixels frame
+                   (lambda (x y c)
+                     (if (> (luminance c) threshold)
+                         c
+                         (rgb 0 0 0)))))
+         (blurred (image:blur bright radius)))
+    (blending:blend-mode frame blurred "add")))