nit(#150): clarify why resolved != symlinkPath in InRepoSymlinkAllowed test

Add a comment explaining that validateDocmapPath calls EvalSymlinks
internally, so the returned path is always the fully-resolved real path
and can never equal the symlink entry itself.

Addresses sonnet bot NIT (review 4810) against d6bab7a9.

cmd/review-bot/validatedocmap_test.go

@@ -687,6 +687,9 @@ func TestValidateDocmapPath_InRepoSymlinkAllowed(t *testing.T) {
 		t.Fatalf("expected in-repo symlink to be accepted, got error: %v", err)
 	}
 	// The returned resolved path must be the real file (not the symlink entry).
+	// validateDocmapPath calls filepath.EvalSymlinks internally, so the returned
+	// path is always the fully-resolved real path — it can never equal the
+	// symlink entry itself.
 	if resolved == symlinkPath {
 		t.Errorf("expected resolved path to differ from symlink path")
 	}