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/layer.sexp

@@ -1,28 +1,36 @@
-;; Layer effect - composite frame-b over frame-a at position
-;; Multi-input effect: uses frame-a (background) and frame-b (overlay)
-;; Params: x, y (position), opacity (0-1), mode (blend mode)
+;; Layer effect - composite overlay over background at position
+;; Streaming-compatible: frame is background, overlay is foreground
+;; Usage: (layer background overlay :x 10 :y 20 :opacity 0.8)
+;;
+;; Params:
+;;   overlay - frame to composite on top
+;;   x, y - position to place overlay
+;;   opacity - blend amount (0-1)
+;;   mode - blend mode (alpha, multiply, screen, etc.)
 
-(require-primitives "image" "blending")
+(require-primitives "image" "blending" "core")
 
 (define-effect layer
   :params (
+    (overlay :type frame :default nil)
     (x :type int :default 0)
     (y :type int :default 0)
     (opacity :type float :default 1.0)
     (mode :type string :default "alpha")
   )
-  (let [bg (copy frame-a)
-        fg frame-b
-        ;; Resize fg if needed to fit
-        fg-w (width fg)
-        fg-h (height fg)]
-    (if (= opacity 1.0)
-      ;; Simple paste
-      (paste bg fg x y)
-      ;; Blend with opacity
-      (let [blended (if (= mode "alpha")
-                      (blend-images (crop bg x y fg-w fg-h) fg opacity)
-                      (blend-images (crop bg x y fg-w fg-h)
-                                   (blend-mode (crop bg x y fg-w fg-h) fg mode)
-                                   opacity))]
-        (paste bg blended x y)))))
+  (if (core:is-nil overlay)
+    frame
+    (let [bg (copy frame)
+          fg overlay
+          fg-w (image:width fg)
+          fg-h (image:height fg)]
+      (if (= opacity 1.0)
+        ;; Simple paste
+        (paste bg fg x y)
+        ;; Blend with opacity
+        (let [blended (if (= mode "alpha")
+                        (blending:blend-images (image:crop bg x y fg-w fg-h) fg opacity)
+                        (blending:blend-images (image:crop bg x y fg-w fg-h)
+                                     (blending:blend-mode (image:crop bg x y fg-w fg-h) fg mode)
+                                     opacity))]
+          (paste bg blended x y))))))