Added UX improvements

[Goldybin]

Summary of Changes:

1. LMStudio Support: Added the lmstudio LLM provider.
2. Multi-Tab System:
   • Server-side session persistence in .apfelstrudel/session.json.
   • Dynamic tab management (create, close, switch, rename).
   • Automatic tab renaming on file open.
3. Undo/Redo System:
   • 100-step history per tab.
   • Automatic backups before AI "Send" and pattern updates.
   • Global keyboard shortcuts (Ctrl+Z, Ctrl+Y).
4. File Operations:
   • "Read from file" (📂) and "Save to file" (💾).
   • Modern File System Access API for the "Save" dialog.
   • Automatic renaming of tabs after opening a file.