launcher: v0.1 — PhotinoNET shell + multi-version orchestration

Single-download .NET 9 self-contained launcher for hosting / joining
DorkNet servers. Reads versions.json from main to discover supported
client builds, fetches the matching server binary + client patcher
from GitHub Releases per branch, manages the server subprocess +
Cloudflare quick-tunnel, and wraps it all in a PhotinoNET window.

Code layout:
- Program.cs           PhotinoNET window + message bridge bootstrap
- Backend/             AppPaths, AppState, VersionsManifest,
                       ReleaseDownloader, ServerProcess, ClientPatcher,
                       Tunnel, RecRoomPicker, JoinCode, MessageBridge
- ui/                  index.html + style.css + app.js (no build step)
- RELEASES.md          GitHub Releases artifact contract per-version
                       branches must publish to

Per-version branches need to ship two release assets per tag:
- dorknet-server-{version_key}-win-x64.zip
- dorknet-clientpatch-{version_key}.zip
(see launcher/RELEASES.md for the full naming + arg contract)

Photon AppIds, JWT secret, and the picked Rec Room path stay
per-machine; the launcher never bundles them.

launcher/Backend/RecRoomPicker.cs

@@ -0,0 +1,41 @@
+using System.Windows.Forms;
+
+namespace DorkNet.Launcher.Backend;
+
+/// <summary>Windows folder picker for the user's
+/// <c>Recroom_Release_Data</c> directory. Per project policy: never
+/// auto-detect via Steam library scanning, always ask the user.</summary>
+public static class RecRoomPicker
+{
+    public static string? Pick(string? initialPath = null)
+    {
+        using var dlg = new FolderBrowserDialog
+        {
+            Description = "Select your Rec Room install's *_Data folder " +
+                          "(e.g. Recroom_Release_Data inside the install).",
+            UseDescriptionForTitle = true,
+            ShowNewFolderButton = false,
+            InitialDirectory = initialPath ?? Environment.GetFolderPath(
+                Environment.SpecialFolder.ProgramFilesX86),
+        };
+        return dlg.ShowDialog() == DialogResult.OK ? dlg.SelectedPath : null;
+    }
+
+    /// <summary>Quick sanity check that the picked path looks like a
+    /// Rec Room install. Doesn't validate the build version — that's
+    /// the patcher's job. Just checks for the canonical files so we
+    /// catch "user picked their Documents folder" mistakes early.</summary>
+    public static (bool ok, string reason) Validate(string path)
+    {
+        if (string.IsNullOrEmpty(path)) return (false, "no path selected");
+        if (!Directory.Exists(path)) return (false, $"folder does not exist: {path}");
+
+        // Recroom_Release_Data/StreamingAssets is the consistent
+        // checkable subfolder across all Rec Room builds we target.
+        var streaming = Path.Combine(path, "StreamingAssets");
+        if (!Directory.Exists(streaming))
+            return (false, "folder is missing StreamingAssets — pick the *_Data folder inside your Rec Room install");
+
+        return (true, "");
+    }
+}