Remove BepInEx client patcher (DorkNet.ClientPatch)

MelonLoader (DorkNet.ClientMod) is the sole client patcher now:

- delete the DorkNet.ClientPatch project + tools/install-plugin.ps1
- drop the project from DorkNet.sln
- README / deploy docs: present DorkNet.ClientMod (install-melon.ps1)
  as the patcher instead of the BepInEx plugin
- drop the dead install-plugin.ps1 reference from Program.cs's JWT
  error and install-melon.ps1's DRM-fallback hint
- tidy stray 'BepInEx port' comments

Legacy-cleanup paths that REMOVE an old BepInEx install
(install-legacy-client.ps1, build-patcher-zip.ps1's old_plugin_paths)
are kept intentionally.

DorkNet.ClientMod/Mod.cs

@@ -1,6 +1,6 @@
-// MelonLoader port of the DorkNet.ClientPatch BepInEx plugin. Applies
-// the minimum set of Harmony patches needed for the 2020 watch to
-// connect to a DorkNet server:
+// DorkNet client mod (MelonLoader IL2CPP). Applies the minimum set of
+// Harmony patches needed for the 2020 watch to connect to a DorkNet
+// server:
 //
 //   1. URI rewrite      — `.rec.net` → user-configured host
 //   2. Photon AppId     — override the baked-in Photon Cloud AppId
@@ -48,11 +48,9 @@ public class Mod : MelonMod
     private int _diagnosticRetryFrame;
     private int _photonOverridePollFrame;
 
-    // Loader-agnostic config — same .Value-shaped accessor the patches
-    // would see in the BepInEx port, just backed by a plain JSON file
-    // instead of BepInEx's TOML config system. Defaults match the BepInEx
-    // plugin's defaults so dropping this mod in without writing a config
-    // file gives the same behaviour as the recommended install.
+    // Config backed by a plain JSON file under MelonLoader/UserData.
+    // The defaults below match the recommended install, so dropping this
+    // mod in without writing a config file still gives working behaviour.
     public static class Cfg
     {
         public static string ServerHost          = "localhost";