Refactor installation and runner scripts for enhanced usability and security

- Updated the installation script to clarify that production wrappers do not include fixed test secrets, improving user guidance for local testing.
- Modified the jiggablend-manager and jiggablend-runner scripts to remove fixed test configurations, emphasizing the use of local test credentials via `make init-test`.
- Enhanced error handling in the runner script to ensure that an API key is provided, improving security and user feedback.
- Added new flags and options for the runner, including sandboxing capabilities and GPU ray tracing control, enhancing flexibility for users.
- Improved README documentation to reflect changes in usage and configuration, ensuring users have clear instructions for setup and execution.

internal/runner/encoding/encoders_test.go

@@ -120,6 +120,10 @@ func TestSoftwareEncoder_BuildCommand_AV1_WithAlpha(t *testing.T) {
 	if !strings.Contains(argsStr, "format=yuva420p10le") {
 		t.Error("Expected tonemap filter to output yuva420p10le for EXR alpha, but not found")
 	}
+	// Alpha VP9/AV1 need -strict experimental on modern FFmpeg
+	if !strings.Contains(argsStr, "-strict experimental") {
+		t.Error("Expected -strict experimental for alpha encode")
+	}
 }
 
 func TestSoftwareEncoder_BuildCommand_VP9(t *testing.T) {