Standardize file permissions using constants and fix parameter ordering inconsistencies

internal/secret/constants.go

@@ -1,5 +1,7 @@
 package secret
 
+import "os"
+
 const (
 	// AppID is the unique identifier for this application
 	AppID = "berlin.sneak.pkg.secret"
@@ -10,3 +12,12 @@ const (
 	EnvUnlockPassphrase = "SB_UNLOCK_PASSPHRASE"
 	EnvGPGKeyID         = "SB_GPG_KEY_ID"
 )
+
+// File system permission constants
+const (
+	// DirPerms is the permission used for directories (read-write-execute for owner only)
+	DirPerms os.FileMode = 0700
+
+	// FilePerms is the permission used for sensitive files (read-write for owner only)
+	FilePerms os.FileMode = 0600
+)