Add welcome popup

[DreamYao520]

What changed

• Added a first-open welcome popup when GuideNH is opened.
• The popup content is loaded from localized resources under assets/guidenh/welcome/ and rendered through the GuideNH page compiler/layout pipeline.
• Added per-player/per-save seen state so the popup only appears once for that player in that save.

## Summary This PR adds a localized first-open welcome popup for GuideNH.

The popup is shown the first time a player opens GuideNH in a save, giving new users a short introduction to what GuideNH is and how to use it. Its content is resource-driven instead of hardcoded, so pack authors can edit or replace the English and Chinese welcome text through localized resources.

The popup uses the existing GuideNH markdown/MDX rendering pipeline, allowing the welcome page to use supported guide syntax such as formatted text, item icons, keybind hints, and other guide components.

A per-player/per-save seen state is added so the popup does not repeatedly appear after it has been dismissed.

Checklist

• I have tested this PR in DevEnv
• I have tested this PR in Fullpack
• This PR is in compliance with the GTNH AI Policy
• This PR requires another PR in order to merge