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/threshold.sexp

@@ -0,0 +1,9 @@
+;; Threshold effect - converts to black and white
+(require-primitives "color_ops")
+
+(define-effect threshold
+  :params (
+    (level :type int :default 128 :range [0 255])
+    (invert :type bool :default false)
+  )
+  (color_ops:threshold frame level invert))