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/README.md

@@ -0,0 +1,19 @@
+# demo
+
+Demo greets people by name.
+
+```go
+import "example.com/docfixture/modules/demo"
+```
+
+## Usage
+
+Call `demo.Hello` or build a `demo.Greeter` and call `demo.Greeter.Greet`.
+
+See the [start guide](../../docs/guide/start.md#install).
+
+## Testing
+
+```sh
+go test ./modules/demo
+```

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)
+}

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

@@ -0,0 +1,13 @@
+package demo
+
+import "testing"
+
+func TestGreet(t *testing.T) {
+	// docs:start greet
+	g := Greeter{Name: "blog"}
+	got := g.Greet()
+	// docs:end greet
+	if got != "Hello, blog" {
+		t.Fatalf("Greet() = %q", got)
+	}
+}

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

@@ -0,0 +1,12 @@
+package demo_test
+
+import (
+	"fmt"
+
+	"example.com/docfixture/modules/demo"
+)
+
+func ExampleHello() {
+	fmt.Println(demo.Hello("blog"))
+	// Output: Hello, blog
+}