Initialize blog scaffold

Add the CLI, site, and sample content so the project can run locally.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/cmd/osaetctl/main.go

@@ -0,0 +1,15 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"osaet/backend/internal/cli"
+)
+
+func main() {
+	if err := cli.Run(os.Args[1:]); err != nil {
+		fmt.Fprintln(os.Stderr, "error:", err)
+		os.Exit(1)
+	}
+}