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/resize-frame.sexp

@@ -0,0 +1,11 @@
+;; Resize effect - replaces RESIZE node
+;; Note: uses target-w/target-h to avoid conflict with width/height primitives
+(require-primitives "image")
+
+(define-effect resize-frame
+  :params (
+    (target-w :type int :default 640 :desc "Target width in pixels")
+    (target-h :type int :default 480 :desc "Target height in pixels")
+    (mode :type string :default "linear" :choices [linear nearest area] :desc "Interpolation mode")
+  )
+  (image:resize frame target-w target-h mode))