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/grayscale.sexp

@@ -0,0 +1,7 @@
+;; Grayscale effect - converts to grayscale
+;; Uses vectorized mix-gray primitive for fast processing
+(require-primitives "image")
+
+(define-effect grayscale
+  :params ()
+  (image:grayscale frame))