feat(installer): record data directory in install manifest

Write the resolved DbPath parent into the manifest so UninstallRunner
can honour customised data locations instead of always assuming
~/.todo-app. Older manifests fall back to the default path.

src/ClaudeDo.Installer/Core/InstallManifest.cs

@@ -8,7 +8,8 @@ public sealed record InstallManifest(
     string Version,
     string InstallDir,
     string WorkerDir,
-    DateTimeOffset InstalledAt);
+    DateTimeOffset InstalledAt,
+    string? DataDir = null);
 
 public static class InstallManifestStore
 {