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/posterize.sexp

@@ -0,0 +1,8 @@
+;; Posterize effect - reduces color levels
+(require-primitives "color_ops")
+
+(define-effect posterize
+  :params (
+    (levels :type int :default 8 :range [2 32])
+  )
+  (color_ops:posterize frame levels))