Add community texture repos and multi-upload custom maps

[0xMDIV]

• Users can now upload multiple custom displacement maps at once — they appear as thumbnails in the preset
  grid for easy switching
• New "Add texture repo" button opens a modal where users can add public GitHub repos containing a
  textures/ folder
• Repo textures are fetched via the GitHub API and displayed alongside built-in presets
• Added repos are listed in the modal and can be removed individually (removes all associated textures
  from the grid)
• Duplicate file uploads and duplicate repos are prevented
• Preset grid is now scrollable (max 5 rows) to keep the sidebar clean
• Custom swatches have a remove button (x) on hover
• All new UI strings translated to EN/DE/IT
• README updated with repo structure requirements, supported formats, and third-party disclaimer
• Everything is session-only — no data is persisted or sent to any server

[CNCKitchen]

I'm a bit worried about copyrighted material here, so I'll postpone this for now. What are your thoughts on this?

[0xMDIV]

sure there could be copyright problems, but thats depending on the repos a user adds, i designed it so every user can add his repos for his own use, so nothing is shared across different sessions.
But yes users have to watch what the add, to make sure that there is no copyright problems is the users choice.