launcher: Rec-Room-styled UI; PowerShell-free patcher; Launch button

UI redesign:
- Warm coral + teal palette over deep purple-navy (closer to Rec Room's
  marketing aesthetic). New wordmark gradient (coral -> pink -> teal).
- Chunky 18px rounded cards on the first-run wizard with per-mode
  accent tinting (coral for host, teal for join) and clear CTAs.
- Form fields wrapped in elevated panels with sectional titles + pill
  status chips in the header (HOST MODE / JOIN MODE / SETTINGS).
- Drop-shadow effects on primary buttons + cards for depth.

Patcher rewrite:
- ClientPatcher.cs no longer shells out to PowerShell; the launcher
  unzips MelonLoader, copies the DorkNet plugin DLL, and renders the
  user-data config template — all in C# in-process.
- Patcher zip now driven by a manifest.json at root (schema v1).
  Per-version branches publish: manifest.json + MelonLoader.zip +
  DorkNet.ClientMod.dll + config template.
- RELEASES.md updated with the new MelonLoader manifest contract and
  the placeholder substitution rules.

Rec Room launch path:
- New Backend/RecRoomLauncher.cs runs Recroom_Release.exe directly
  from the picked install folder's parent dir (no Steam).
- 'Launch Rec Room' button appears after a successful patch in both
  host + join modes.

launcher/Backend/RecRoomLauncher.cs

@@ -0,0 +1,51 @@
+using System.Diagnostics;
+using System.IO;
+
+namespace DorkNet.Launcher.Backend;
+
+/// <summary>Launches the user's already-patched Rec Room install
+/// directly via <c>Recroom_Release.exe</c>. Never goes through Steam —
+/// DorkNet users may not own the game on Steam.</summary>
+public static class RecRoomLauncher
+{
+    /// <summary>The picked install path is the <c>Recroom_Release_Data</c>
+    /// folder; the executable lives at <c>&lt;parent&gt;\Recroom_Release.exe</c>.
+    /// Returns true if Process.Start succeeded.</summary>
+    public static bool TryLaunch(string recRoomDataPath, out string error)
+    {
+        error = "";
+        if (string.IsNullOrEmpty(recRoomDataPath))
+        {
+            error = "No Rec Room install picked.";
+            return false;
+        }
+        var parent = Path.GetDirectoryName(recRoomDataPath.TrimEnd(Path.DirectorySeparatorChar));
+        if (string.IsNullOrEmpty(parent))
+        {
+            error = $"Couldn't resolve the parent directory of '{recRoomDataPath}'.";
+            return false;
+        }
+        var exe = Path.Combine(parent, "Recroom_Release.exe");
+        if (!File.Exists(exe))
+        {
+            error = $"Recroom_Release.exe not found at '{exe}'. " +
+                    "Pick the *_Data folder that sits next to it.";
+            return false;
+        }
+        try
+        {
+            Process.Start(new ProcessStartInfo
+            {
+                FileName = exe,
+                WorkingDirectory = parent,
+                UseShellExecute = true,
+            });
+            return true;
+        }
+        catch (Exception ex)
+        {
+            error = ex.Message;
+            return false;
+        }
+    }
+}