launcher: grandma-proof batch 1 — auto-detect + LAN mode

- RecRoomPicker.Detect: scan common manual-install paths (Documents/Recnet/dist, Downloads, C:\Games, etc.) on first run; never touches Steam libraries per policy
- RecRoomVersionDetector: three-signal cascade (version.txt -> PE timestamp -> file size) maps install to a manifest branch so version dropdown defaults correctly
- CloudflaredInstaller: download latest cloudflared-windows-amd64.exe from GitHub releases to %LOCALAPPDATA%\DorkNet on first host; resolves side-by-side -> cache -> PATH -> download
- LocalNetwork.GetLanIp + AppState.HostingMode (Internet|LocalNetwork) + Host view "WHO CAN JOIN?" radio: LAN-only mode skips Cloudflare entirely for families on one network
- OnHostStart branches on HostingMode; status text reflects local IP vs public tunnel URL

launcher/MainWindow.xaml

@@ -155,7 +155,19 @@
                                          LostFocus="OnServerNameChanged" />
 
                                 <TextBlock Style="{StaticResource FieldLabel}" Text="REC ROOM VERSION TO HOST FOR" />
-                                <ComboBox x:Name="VersionSelect" />
+                                <ComboBox x:Name="VersionSelect" Margin="0,0,0,16" />
+
+                                <TextBlock Style="{StaticResource FieldLabel}" Text="WHO CAN JOIN?" />
+                                <StackPanel Orientation="Horizontal">
+                                    <RadioButton x:Name="HostModeInternet" GroupName="HostingMode"
+                                                 Content="Friends anywhere (internet via Cloudflare)"
+                                                 IsChecked="True" Checked="OnHostingModeChanged"
+                                                 Foreground="{StaticResource Ink}" />
+                                    <RadioButton x:Name="HostModeLocal" GroupName="HostingMode"
+                                                 Content="Same WiFi only (no internet needed)"
+                                                 Margin="22,0,0,0" Checked="OnHostingModeChanged"
+                                                 Foreground="{StaticResource Ink}" />
+                                </StackPanel>
                             </StackPanel>
                         </Border>