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/l1/sexp_effects/effects/emboss.sexp

@@ -0,0 +1,13 @@
+;; Emboss effect - creates raised/3D appearance
+(require-primitives "blending")
+
+(define-effect emboss
+  :params (
+    (strength :type int :default 1 :range [0.5 3])
+    (blend :type float :default 0.3 :range [0 1])
+  )
+  (let* ((kernel (list (list (- strength) (- strength) 0)
+                       (list (- strength) 1 strength)
+                       (list 0 strength strength)))
+         (embossed (convolve frame kernel)))
+    (blending:blend-images embossed frame blend)))