Fix Snapmaker account login not persisting across restarts

[amitamit10]

Summary

Fixes #669 (and the same underlying cause behind the related reports in #226, #116, and #716).

The native SMUserInfo struct (m_login_userinfo), which backs sw_GetUserLoginState for the embedded Flutter login webview, was only ever populated in-memory during an active login flow (WebSMUserLoginDialog::OnNavigationRequest) and was never written to or restored from AppConfig. Every app restart therefore started with an empty, logged-out struct — regardless of whether the embedded webview's own localStorage still had a cached token — so the login screen reappeared on every launch even though the account token itself was still valid.

This was reproducible outside the Flatpak sandbox too (confirmed on a from-source Linux build), which rules out sandbox/permission causes such as keyring access or the webview's local-server port.

Platform scope

All existing reports of this symptom are Linux-only, but the affected code (WebSMUserLoginDialog::OnNavigationRequest, GUI_App::sm_get_login_info, the SMUserInfo struct) has no #ifdef _WIN32 / __APPLE__ guards anywhere — it's plain cross-platform C++ shared by every build. The native "am I logged in" check always reads from m_login_userinfo, which resets to its default (logged-out) state on every process launch regardless of OS or webview backend (WebKitGTK/WebView2/WKWebView). I don't have a Windows or macOS machine to confirm directly, but nothing in the code path is platform-specific, so this likely affects those builds too, just underreported so far.

Fix

• On successful login (WebSMUserLoginDialog.cpp), persist token/account/nickname/icon/id to a new sm_user AppConfig section and save immediately.
• On startup (GUI_App.cpp), right after AppConfig::load() and before the webview's first sw_GetUserLoginState call, restore the saved session into m_login_userinfo if a token is present.
• On logout (sm_request_user_logout), clear the persisted sm_user.token so a revoked session isn't restored on next launch.

Test plan

• Built from source on Linux (Ubuntu 24.04), logged in via Login/Register
• Confirmed sm_user section written to AppConfig (~/.config/Snapmaker_Orca/Snapmaker_Orca.conf) with token/account/nickname/icon/id
• Fully quit the app, relaunched — session restored, sidebar shows the logged-in account instead of Login/Register
• Repeated across multiple restarts, consistent
• Not yet verified on Windows/macOS — the fix touches shared, platform-agnostic code, so it should apply, but a maintainer/tester with those platforms should confirm