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/Steps/WriteInstallManifestStep.cs

@@ -1,4 +1,5 @@
 using System.IO;
+using ClaudeDo.Data;
 using ClaudeDo.Installer.Core;
 
 namespace ClaudeDo.Installer.Steps;
@@ -14,11 +15,14 @@ public sealed class WriteInstallManifestStep : IInstallStep
 
         try
         {
+            var dataDir = Path.GetDirectoryName(Paths.Expand(ctx.DbPath));
+
             var manifest = new InstallManifest(
                 Version: ctx.InstalledVersion,
                 InstallDir: ctx.InstallDirectory,
                 WorkerDir: Path.Combine(ctx.InstallDirectory, "worker"),
-                InstalledAt: DateTimeOffset.UtcNow);
+                InstalledAt: DateTimeOffset.UtcNow,
+                DataDir: dataDir);
 
             InstallManifestStore.Write(ctx.InstallDirectory, manifest);
             progress.Report($"Wrote {InstallManifestStore.ManifestPath(ctx.InstallDirectory)}");