refactor(config): consolidate permission modes into PermissionModeRegistry

Also fixes WorkerHub.UpdateAppSettings falling back to "bypassPermissions"
when AppSettingsEntity and the runtime default are "auto". The fallback
now matches the entity default.

src/ClaudeDo.Data/Models/PermissionModeRegistry.cs

@@ -0,0 +1,11 @@
+namespace ClaudeDo.Data.Models;
+
+public static class PermissionModeRegistry
+{
+    public static readonly IReadOnlyList<string> Modes = new[]
+    {
+        "auto", "bypassPermissions", "acceptEdits", "plan", "default",
+    };
+
+    public const string DefaultMode = "auto";
+}