Replace batch DAG system with streaming architecture

- Remove legacy_tasks.py, hybrid_state.py, render.py
- Remove old task modules (analyze, execute, execute_sexp, orchestrate)
- Add streaming interpreter from test repo
- Add sexp_effects with primitives and video effects
- Add streaming Celery task with CID-based asset resolution
- Support both CID and friendly name references for assets
- Add .dockerignore to prevent local clones from conflicting

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

sexp_effects/effects/echo.sexp

@@ -0,0 +1,19 @@
+;; Echo effect - motion trails using frame buffer
+(require-primitives "blending")
+
+(define-effect echo
+  :params (
+    (num_echoes :type int :default 4 :range [1 20])
+    (decay :type float :default 0.5 :range [0 1])
+  )
+  (let* ((buffer (state-get 'buffer (list)))
+         (new-buffer (take (cons frame buffer) (+ num_echoes 1))))
+    (begin
+      (state-set 'buffer new-buffer)
+      ;; Blend frames with decay
+      (if (< (length new-buffer) 2)
+          frame
+          (let ((result (copy frame)))
+            ;; Simple blend of first two frames for now
+            ;; Full version would fold over all frames
+            (blending:blend-images frame (nth new-buffer 1) (* decay 0.5)))))))