feat(11.1-02): check links, commands, forbidden names and fence policy

- relative links and anchors resolve against the renderer's heading IDs
- summer and ./bin/<app> command names come from the real command
  constructors through docsite.Options.Commands; a nil set is a problem
- consuming-application names fail in page sources and built outputs
- go fences in docs/ pages need src=, callouts are NOTE, TIP or WARNING,
  docs/ headings are plain ASCII
- gate gains --claude and self-test plants for each new rule

cmd/summer/main_test.go

@@ -89,7 +89,7 @@ func TestToolDoesNotImportExamplePlugins(t *testing.T) {
 				if err != nil {
 					t.Fatal(err)
 				}
-				if strings.Contains(path, "examples/hello") || strings.Contains(path, "golem15/fonoteka") {
+				if strings.Contains(path, "examples/hello") || strings.Contains(path, "docs/examples") || strings.Contains(path, "golem15/fonoteka") {
 					t.Fatalf("%s imports %s", name, path)
 				}
 			}