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/templates/crossfade-zoom.sexp

@@ -0,0 +1,25 @@
+;; Crossfade with Zoom Transition
+;;
+;; Macro for transitioning between two frames with a zoom effect.
+;; Active frame zooms out while next frame zooms in.
+;;
+;; Required context:
+;;   - zoom effect must be loaded
+;;   - blend effect must be loaded
+;;
+;; Parameters:
+;;   active-frame: current frame
+;;   next-frame: frame to transition to
+;;   fade-amt: transition progress (0 = all active, 1 = all next)
+;;
+;; Usage:
+;;   (include :path "../templates/crossfade-zoom.sexp")
+;;   ...
+;;   (crossfade-zoom active-frame next-frame 0.5)
+
+(defmacro crossfade-zoom (active-frame next-frame fade-amt)
+  (let [active-zoom (+ 1.0 fade-amt)
+        active-zoomed (zoom active-frame :amount active-zoom)
+        next-zoom (+ 0.1 (* fade-amt 0.9))
+        next-zoomed (zoom next-frame :amount next-zoom)]
+    (blend active-zoomed next-zoomed :opacity fade-amt)))