Fix GPU encoding black frames and improve debug logging

- Add CUDA sync before encoding to ensure RGB->NV12 kernel completes
- Add debug logging for frame data validation (sum check)
- Handle GPUFrame objects in GPUHLSOutput.write()
- Fix cv2.resize for CuPy arrays (use cupyx.scipy.ndimage.zoom)
- Fix fused pipeline parameter ordering (geometric first, color second)
- Add raindrop-style ripple with random position/freq/decay/amp
- Generate final VOD playlist with #EXT-X-ENDLIST

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

streaming/stream_sexp_generic.py

@@ -144,8 +144,7 @@ class StreamInterpreter:
         """Load a config file and process its definitions."""
         config_path = Path(config_path)  # Accept str or Path
         if not config_path.exists():
-            print(f"Warning: config file not found: {config_path}", file=sys.stderr)
-            return
+            raise FileNotFoundError(f"Config file not found: {config_path}")
 
         text = config_path.read_text()
         ast = parse_all(text)
@@ -221,8 +220,7 @@ class StreamInterpreter:
                 break
 
         if not lib_path:
-            print(f"Warning: primitive library '{lib_name}' not found", file=sys.stderr)
-            return
+            raise FileNotFoundError(f"Primitive library '{lib_name}' not found. Searched paths: {lib_paths}")
 
         spec = importlib.util.spec_from_file_location(actual_lib_name, lib_path)
         module = importlib.util.module_from_spec(spec)
@@ -262,8 +260,7 @@ class StreamInterpreter:
     def _load_effect(self, effect_path: Path):
         """Load and register an effect from a .sexp file."""
         if not effect_path.exists():
-            print(f"Warning: effect file not found: {effect_path}", file=sys.stderr)
-            return
+            raise FileNotFoundError(f"Effect/include file not found: {effect_path}")
 
         text = effect_path.read_text()
         ast = parse_all(text)
@@ -938,8 +935,7 @@ class StreamInterpreter:
                 audio = str(resolved)
                 print(f"Lazy resolved audio: {audio}", file=sys.stderr)
             else:
-                print(f"WARNING: Audio file not found: {audio}", file=sys.stderr)
-                audio = None
+                raise FileNotFoundError(f"Audio file not found: {audio}")
         if output == "pipe":
             out = PipeOutput(size=(w, h), fps=fps, audio_source=audio)
         elif output == "preview":