Add generic streaming interpreter with configurable sources/audio

- Add stream_sexp_generic.py: fully generic sexp interpreter
- Add streaming primitives for video sources and audio analysis
- Add config system for external sources and audio files
- Add templates for reusable scans and macros
- Fix video/audio stream mapping in file output
- Add dynamic source cycling based on sources array length
- Remove old Python effect files (migrated to sexp)
- Update sexp effects to use namespaced primitives

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

sexp_effects/effects/posterize.sexp

@@ -1,12 +1,8 @@
 ;; Posterize effect - reduces color levels
+(require-primitives "color_ops")
 
 (define-effect posterize
   :params (
     (levels :type int :default 8 :range [2 32])
   )
-  (let ((step (floor (/ 256 levels))))
-    (map-pixels frame
-      (lambda (x y c)
-        (rgb (* (floor (/ (red c) step)) step)
-             (* (floor (/ (green c) step)) step)
-             (* (floor (/ (blue c) step)) step))))))
+  (color_ops:posterize frame levels))