fix(onboard): skip legacy AGENT.md when copying embedded workspace templates

The workspace/ directory contains both AGENT.md (legacy) and AGENTS.md
(current). copyEmbeddedToTarget was copying both, causing the test
TestCopyEmbeddedToTargetUsesAgentsMarkdown to fail. Skip AGENT.md
during the walk to match the expected behavior.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/picoclaw/internal/onboard/helpers.go

@@ -70,6 +70,11 @@ func copyEmbeddedToTarget(targetDir string) error {
 			return nil
 		}
 
+		// Skip legacy file superseded by AGENTS.md
+		if filepath.Base(path) == "AGENT.md" {
+			return nil
+		}
+
 		// Read embedded file
 		data, err := embeddedFiles.ReadFile(path)
 		if err != nil {