Prevent test pollution in production database (bd-z528)

- Add warning when creating issues with 'Test' prefix
- Suggest BEADS_DB for isolated testing
- Document testing workflow in AGENTS.md
- Include examples for manual and automated testing

Amp-Thread-ID: https://ampcode.com/threads/T-fc7b7391-8881-4dd9-8e1f-28a2f95afb2b
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/create.go

@@ -57,6 +57,13 @@ var createCmd = &cobra.Command{
 			os.Exit(1)
 		}
 
+		// Warn if creating a test issue in production database
+		if strings.HasPrefix(strings.ToLower(title), "test") {
+			yellow := color.New(color.FgYellow).SprintFunc()
+			fmt.Fprintf(os.Stderr, "%s Creating issue with 'Test' prefix in production database.\n", yellow("⚠"))
+			fmt.Fprintf(os.Stderr, "  For testing, consider using: BEADS_DB=/tmp/test.db ./bd create \"Test issue\"\n")
+		}
+
 		// Load template if specified
 		var tmpl *Template
 		if fromTemplate != "" {