Add LAN discovery and Local servers UI

Adds LAN server discovery and a Local tab in the multiplayer UI so clients can find relays on the same LAN. Introduces a new F4T::LanDiscovery module (plugin/include/F4TLanDiscovery.h, plugin/src/F4TLanDiscovery.cpp) that probes LAN hosts via UDP discover (port 7778) and TCP welcome fallback (port 7777). Server-side support includes a UDP responder (server/lan_discovery.py) and integration in server_core.py to start/stop discovery.

Plugin changes (F4TServerBrowserBridge/Data) add background scanning, dispatch results to the game thread, new local-server storage and events (scanLocalServers, localServersUpdated, localScanStarted/localScanFinished), and small join/recent handling updates. UI changes (ui/.../app.js and components) add localServers state, scanning UX, Recent persistence (localStorage), and join logic for local/direct entries. Docs updated (docs/protocol.md, docs/dev-log.md, server/README.md) and build script links iphlpapi. Also removes two unused exported sprite PNGs.

ui/views/CommonwealthOnline/browser/index.html

@@ -43,6 +43,19 @@
               </div>
             </div>
 
+            <div class="co-tab-pane" data-pane="local">
+              <header class="co-subpanel-header">
+                <h2 class="co-subpanel-title" id="coLocalTitle">Local Servers</h2>
+                <div class="co-subpanel-meta">
+                  <span class="co-count" id="coLocalCount"></span>
+                </div>
+              </header>
+              <div class="co-server-list-wrap">
+                <div class="co-server-list co-local-list"></div>
+                <div class="co-scroll-indicator" aria-hidden="true">&raquo;&raquo;</div>
+              </div>
+            </div>
+
             <div class="co-tab-pane" data-pane="favorites">
               <header class="co-subpanel-header">
                 <h2 class="co-subpanel-title">Favorites</h2>