Document design choices and standardize Dockerfile

cmd/pysentry/main.go

@@ -3,5 +3,8 @@ package main
 import "github.com/pysentry/pysentry/src/gui"
 
 func main() {
+	// The executable entry point intentionally delegates all startup work to the
+	// GUI package. Keeping main small makes it easier to add platform-specific
+	// packaging later without mixing window setup, storage, and scheduler logic.
 	gui.Run()
 }