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/internal/cli/config_test.go

@@ -0,0 +1,33 @@
+package cli
+
+import "testing"
+
+func TestChangedConfigFields(t *testing.T) {
+	var a siteConfigFile
+	a.Meta.ConfigVersion = 1
+	a.Meta.UpdatedAt = "2026-05-28T12:00:00+08:00"
+	a.Site.Title = "A"
+	a.Content.PostsDir = "content/posts"
+	a.Build.OutputDir = "dist/site"
+
+	b := a
+	if fields := changedConfigFields(a, b); len(fields) != 0 {
+		t.Fatalf("unchanged config fields = %#v", fields)
+	}
+
+	b.Site.Title = "B"
+	b.Build.OutputDir = "dist/other"
+	fields := changedConfigFields(a, b)
+	if len(fields) != 2 || fields[0] != "site.title" || fields[1] != "build.output_dir" {
+		t.Fatalf("changed fields = %#v", fields)
+	}
+}
+
+func TestParseTime(t *testing.T) {
+	if _, ok := parseTime("2026-05-28T12:00:00+08:00"); !ok {
+		t.Fatal("expected RFC3339 time to parse")
+	}
+	if _, ok := parseTime("not-time"); ok {
+		t.Fatal("expected invalid time")
+	}
+}