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/echo.sexp

@@ -1,4 +1,5 @@
 ;; Echo effect - motion trails using frame buffer
+(require-primitives "blending")
 
 (define-effect echo
   :params (
@@ -15,4 +16,4 @@
           (let ((result (copy frame)))
             ;; Simple blend of first two frames for now
             ;; Full version would fold over all frames
-            (blend-images frame (nth new-buffer 1) (* decay 0.5)))))))
+            (blending:blend-images frame (nth new-buffer 1) (* decay 0.5)))))))