fix: add language labels to fenced code blocks for MD040 compliance

Add `text` language identifier to unlabeled fenced code blocks
to satisfy markdownlint MD040 rule across Go documentation files.

skills/golang-patterns/SKILL.md

@@ -364,7 +364,7 @@ func WriteAndFlush(w io.Writer, data []byte) error {
 
 ### Standard Project Layout
 
-```
+```text
 myproject/
 ├── cmd/
 │   └── myapp/