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/docs/extras/faq.md

@@ -0,0 +1,15 @@
+---
+title: FAQ
+description: "Questions about the demo."
+section: extras
+order: 20
+---
+# FAQ
+
+## Does it migrate
+
+Yes, run `./bin/demo migrate`, then `summer docs:sync` after a source change.
+
+```text
+summer not:checked in a text fence
+```

internal/docsite/testdata/clean/docs/extras/usage.md

@@ -0,0 +1,18 @@
+---
+title: Usage
+description: "Build a greeter and call it."
+section: extras
+order: 10
+---
+# Usage
+
+## Call it
+
+A `demo.Greeter` greets by name:
+
+```go src=modules/demo/demo_test.go#greet
+g := Greeter{Name: "blog"}
+got := g.Greet()
+```
+
+See [Greet someone](../guide/start.md#greet-someone).