Add server validation, profile store, session launch

Introduce server validation and a session launch flow with persistent server profiles.

- Add ConnectAndValidateServer to Networking to validate handshake/timeouts and return human-friendly errors; avoid auto-connecting in transform send path and remove unconditional local connect on startup.
- Add ServerProfileStore (header + implementation) to persist server->saveFile bindings under Documents/My Games/.../CommonwealthOnline/server-profiles.json with thread-safe load/save, lookup, touch and bind operations.
- Add SessionLaunch (header + implementation) to handle launching validated sessions, first-time join flow (auto coc to SanctuaryExt, character creation menus, save binding), F4SE message handling and periodic Update processing.
- Update ServerBrowserBridge to parse/validate ports, use ConnectAndValidateServer, display joinLoading UI events, schedule validated session launch on the game task thread, and centralize join success/failure handling.
- Wire SessionLaunch into main.cpp (update loop and F4SE message hook).
- Improve direct-connect UI in app.js with client-side validation, port parsing, and handling of joinLoading events.

These changes provide better connection validation, user feedback during joins, and automatic handling for first-time server joins with persistence of associated saves.

plugin/include/F4TNetworking.h

@@ -8,6 +8,7 @@ namespace F4T::Networking
 	std::string GetLocalPlayerLogPrefix();
 	bool ConnectToServer(const char* a_host, std::uint16_t a_port);
 	bool ConnectToLocalServer();
+	bool ConnectAndValidateServer(const char* a_host, std::uint16_t a_port, std::string& a_error);
 	void DisconnectFromLocalServer();
 	bool IsConnectedToServer();
 	bool SendTransformPacket(

plugin/include/F4TServerProfileStore.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <cstdint>
+#include <optional>
+#include <string>
+
+namespace F4T::ServerProfileStore
+{
+	std::string MakeServerKey(const std::string& a_host, std::uint16_t a_port);
+
+	bool HasProfile(const std::string& a_serverKey);
+	std::optional<std::string> LookupSaveFile(const std::string& a_serverKey);
+	void BindSaveFile(const std::string& a_serverKey, const std::string& a_saveFile);
+	void TouchProfile(const std::string& a_serverKey);
+}

plugin/include/F4TSessionLaunch.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include "F4TServerBrowserData.h"
+
+namespace F4SE
+{
+	class MessagingInterface;
+}
+
+namespace F4T::SessionLaunch
+{
+	bool LaunchValidatedSession(const ServerBrowser::ServerEntry& a_entry, std::string& a_error);
+	void OnF4SEMessage(F4SE::MessagingInterface::Message* a_msg);
+	void Update();
+	void TryCompletePendingProfileBind();
+}