launcher: side-by-side versions.json fallback + empty-state UX

The version dropdown sat silently empty when the GitHub manifest
fetch 404'd (private repo, network down, etc.) and there was no
DORKNET_LOCAL_MANIFEST to fall back to. Two fixes:

- csproj copies the repo-root versions.json next to dorknet.exe on
  build, and LocalOverrides.GetLocalManifestPath checks that path
  as a fallback after the env var. Dev checkouts against a private
  repo now Just Work — no env vars needed.
- When the manifest can't be loaded, RefreshManifestAsync now
  inserts a disabled placeholder "(no versions - check internet or
  set DORKNET_LOCAL_MANIFEST)" in the dropdown so the user sees the
  problem at a glance instead of a silent blank.
- LocalOverrides.DescribeManifestSource shows in Settings whether
  the active manifest came from the env var, the side-by-side
  fallback, or the live GitHub fetch.

launcher/Backend/LocalOverrides.cs

@@ -26,14 +26,21 @@ public static class LocalOverrides
     public const string ManifestEnvVar = "DORKNET_LOCAL_MANIFEST";
     public const string ReleasesEnvVar = "DORKNET_LOCAL_RELEASES";
 
-    /// <summary>Returns the configured manifest path if the env var is
-    /// set AND the file exists; null otherwise. Caller decides whether
-    /// to fall back to the network.</summary>
+    /// <summary>Returns a local manifest path to use instead of the
+    /// GitHub fetch. Prefers <c>DORKNET_LOCAL_MANIFEST</c> when set; if
+    /// that's unset, falls back to a side-by-side <c>versions.json</c>
+    /// next to <c>dorknet.exe</c> (so dev checkouts against a private
+    /// repo work without env-var wiring — the launcher's csproj copies
+    /// the repo-root versions.json to its bin output on build).</summary>
     public static string? GetLocalManifestPath()
     {
         var path = Environment.GetEnvironmentVariable(ManifestEnvVar);
-        if (string.IsNullOrEmpty(path)) return null;
-        return File.Exists(path) ? path : null;
+        if (!string.IsNullOrEmpty(path) && File.Exists(path)) return path;
+
+        var sideBySide = Path.Combine(AppContext.BaseDirectory, "versions.json");
+        if (File.Exists(sideBySide)) return sideBySide;
+
+        return null;
     }
 
     /// <summary>Returns the configured releases-root if the env var is
@@ -87,4 +94,23 @@ public static class LocalOverrides
             ? $"{envVar} -> {raw}  [active]"
             : $"{envVar} -> {raw}  [SET BUT NOT FOUND on disk]");
     }
+
+    /// <summary>Best-effort description of where the manifest is
+    /// actually coming from this session. Mainly for the Settings UI
+    /// so the user can tell at a glance "side-by-side dev manifest"
+    /// vs "live GitHub fetch" vs "broken env-var path".</summary>
+    public static string DescribeManifestSource()
+    {
+        var env = Environment.GetEnvironmentVariable(ManifestEnvVar);
+        if (!string.IsNullOrEmpty(env))
+        {
+            return File.Exists(env)
+                ? $"manifest source: {env} (env var)"
+                : $"manifest source: {env} (env var, NOT FOUND — falling back)";
+        }
+        var sideBySide = Path.Combine(AppContext.BaseDirectory, "versions.json");
+        if (File.Exists(sideBySide))
+            return $"manifest source: {sideBySide} (side-by-side fallback)";
+        return "manifest source: live GitHub fetch (no local override)";
+    }
 }

launcher/DorkNet.Launcher.csproj

@@ -27,4 +27,17 @@
     <PackageReference Include="QRCoder" Version="1.6.0" />
   </ItemGroup>
 
+  <!-- Dev convenience: copy the repo-root versions.json next to dorknet.exe
+       on build, so a dev checkout works against the private repo without
+       needing DORKNET_LOCAL_MANIFEST set. LocalOverrides picks this up as
+       a side-by-side fallback. The file is harmless to ship in release
+       builds too — VersionsManifest still prefers the live GitHub fetch
+       when reachable. -->
+  <ItemGroup>
+    <None Include="..\versions.json" Condition="Exists('..\versions.json')">
+      <Link>versions.json</Link>
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
 </Project>

launcher/MainWindow.xaml.cs

@@ -184,13 +184,25 @@ public partial class MainWindow : Window
     private async Task RefreshManifestAsync()
     {
         _manifest = await new VersionsManifest().FetchAsync();
+        VersionSelect.Items.Clear();
         if (_manifest is null)
         {
-            HostStatusText.Text = "Couldn't load versions.json from GitHub. " +
-                "Check internet, then reopen.";
+            // Empty placeholder so the user sees *something* in the
+            // dropdown instead of a silent blank — helps when the public
+            // repo is unreachable (e.g. private repo + no env override).
+            var placeholder = new ComboBoxItem
+            {
+                Content = "(no versions — check internet or set DORKNET_LOCAL_MANIFEST)",
+                IsEnabled = false,
+                Tag = null,
+            };
+            VersionSelect.Items.Add(placeholder);
+            placeholder.IsSelected = true;
+            HostStatusText.Text = "Couldn't load versions.json. " +
+                "Either the repo isn't reachable, or DORKNET_LOCAL_MANIFEST " +
+                "points at a missing/invalid file — check Settings.";
             return;
         }
-        VersionSelect.Items.Clear();
         foreach (var v in _manifest.Branches.Where(b => b.Supported))
         {
             var item = new ComboBoxItem