feat(11.1-03): add the Coming from WinterCMS concept map with a verified plugin example

- docs/setup/coming-from-wintercms.md maps WinterCMS concepts to checked
  pkg.Ident spans and lists what SummerCMS does not provide
- party BlogPlugin and ExamplePlugin, shown through src= fences
- TestDocsRequiredPages asserts required pages build as .html and .md
- index links the new page

cmd/summer/docs_test.go

@@ -72,6 +72,38 @@ func TestDocsBuildRealTree(t *testing.T) {
 	}
 }
 
+// requiredPages lists the guide pages the docs must keep. Each content plan
+// appends the pages it writes.
+var requiredPages = []string{
+	"index",
+	"setup/installation",
+	"setup/coming-from-wintercms",
+}
+
+// TestDocsRequiredPages asserts that every required page is in the loaded
+// tree and is built as both .html and .md on the real tree.
+func TestDocsRequiredPages(t *testing.T) {
+	pages, problems, err := docsite.Pages(docsite.Options{Root: repoRoot, Commands: docsCommands()})
+	if err != nil || len(problems) > 0 {
+		t.Fatalf("Pages: %v %v", err, problems)
+	}
+	loaded := map[string]bool{}
+	for _, p := range pages {
+		loaded[p.URL] = true
+	}
+	out, _ := buildRealTree(t)
+	for _, url := range requiredPages {
+		if !loaded[url] {
+			t.Errorf("page %s is not in the docs tree", url)
+		}
+		for _, ext := range []string{".html", ".md"} {
+			if _, err := os.Stat(filepath.Join(out, filepath.FromSlash(url)+ext)); err != nil {
+				t.Errorf("page %s has no %s output: %v", url, ext, err)
+			}
+		}
+	}
+}
+
 // frameworkModules lists modules/<m> directories that hold a non-test Go
 // file, discovered independently of docsite.
 func frameworkModules(t *testing.T) []string {