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.

commands/go-build.md

@@ -43,7 +43,7 @@ go mod tidy -v
 
 ## Example Session
 
-```
+```text
 User: /go-build
 
 Agent:

commands/go-review.md

@@ -68,7 +68,7 @@ govulncheck ./...
 
 ## Example Usage
 
-```
+```text
 User: /go-review
 
 Agent:

commands/go-test.md

@@ -35,7 +35,7 @@ REPEAT  → Next test case
 
 ## Example Session
 
-```
+```text
 User: /go-test I need a function to validate email addresses
 
 Agent: