refactor(installer): drop self-update, publish stable-named ClaudeDo.Installer.exe

Release workflow now names the installer asset ClaudeDo.Installer.exe (no version) for a permanent download URL; it is still uploaded and checksummed on every release. App + worker keep the git tag version.

Removes the self-update preflight from App.OnStartup and deletes the now-dead SelfUpdater / SelfUpdatePromptWindow / SelfUpdateResult plus their tests. App-update detection is unaffected: the manifest records the release tag via DownloadAndExtractStep.

Updates the installer CLAUDE.md.

src/ClaudeDo.Installer/Steps/WriteUninstallRegistryStep.cs

@@ -26,9 +26,9 @@ public sealed class WriteUninstallRegistryStep : IInstallStep
         // the single-file temp extract is gone once this process exits.
         var sourceExe = Environment.ProcessPath
             ?? throw new InvalidOperationException("Cannot resolve running installer path.");
-        // In the self-update path the installer already runs from uninstaller/ (the
-        // --replace-self handoff put it there), so source == target and the copy would
-        // throw. Skip it; the binary is already in place.
+        // When relaunched from the installed copy (e.g. the Apps & Features "Rerun
+        // Installer" entry points at uninstaller/ClaudeDo.Installer.exe), source == target
+        // and the copy would throw. Skip it; the binary is already in place.
         var alreadyInPlace = string.Equals(
             Path.GetFullPath(sourceExe), Path.GetFullPath(targetExe), StringComparison.OrdinalIgnoreCase);
         if (!alreadyInPlace)