test(11.1-06): plant one fixture per docs checker rule and run them in the gate

- testdata/clean passes every check; 63 violation cases each overlay one
  fault and a want.txt naming the single problem it must produce
- TestPlantedViolations also plants the forbidden name (split literals)
  and symlink escapes at run time; TestBuildOutputGuard covers --out
- check-phase11.1.sh --self-test runs the corpus through a go test -json
  detector that refuses FAIL, SKIP, zero tests and no tests to run
- the self-test scratch copy now carries examples/ and README.md, so its
  baseline sees the example command literals the real tree sees

internal/docsite/testdata/clean/modules/demo/demo.go

@@ -0,0 +1,17 @@
+// Package demo is the docs checker fixture module.
+package demo
+
+// Hello returns a greeting for name.
+func Hello(name string) string {
+	return "Hello, " + name
+}
+
+// Greeter greets by name.
+type Greeter struct {
+	Name string
+}
+
+// Greet returns the greeting for the greeter's name.
+func (g Greeter) Greet() string {
+	return Hello(g.Name)
+}