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

internal/docsite/load.go

@@ -195,6 +195,7 @@ func assemble(opts Options) (*site, []Problem, error) {
 			return nil, nil, err
 		}
 		problems = append(problems, rp...)
+		problems = append(problems, s.checkForbiddenOutputs()...)
 	}
 	sortProblems(problems)
 	return s, problems, nil