Add GUI desktop application

- Add gui/ package: CustomTkinter app with dashboard, mods, tools, logs,
  and settings views; first-run SetupWizard for config.json generation
- Add gui.py root entry point (calls gui.run_app())
- Add selection.json for GUI selection state persistence
- Add customtkinter to requirements.txt
- Fix link_mods.py minor issues surfaced during GUI integration
- Add modlist_html/Test_Preset_A.html and Test_Preset_B.html as example inputs
- Update README.md: add GUI prerequisites, gui.py script section, gui/ folder
  structure, customtkinter to prerequisites table
- Update CLAUDE.md: add python gui.py to common commands, document GUI package
  architecture and views

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

link_mods.py

@@ -99,7 +99,7 @@ def cmd_link(cfg, group: str) -> None:
     print()
 
 
-def cmd_unlink(cfg, group: str) -> None:
+def cmd_unlink(cfg, group: str, yes: bool = False) -> None:
     group_dir = cfg.downloads / group
     if not group_dir.is_dir():
         print(f"ERROR: group folder not found: {group_dir}")
@@ -118,10 +118,13 @@ def cmd_unlink(cfg, group: str) -> None:
     print(f"    Group: {group}  ({linked_count} linked mod(s))")
     print()
 
-    choice = input("  Continue? [y/N]: ").strip().lower()
-    if choice not in ("y", "yes"):
-        print("  Aborted.\n")
-        sys.exit(0)
+    if yes:
+        print("  (--yes flag set — skipping confirmation)")
+    else:
+        choice = input("  Continue? [y/N]: ").strip().lower()
+        if choice not in ("y", "yes"):
+            print("  Aborted.\n")
+            sys.exit(0)
 
     print()
 
@@ -158,6 +161,8 @@ def main() -> None:
     )
     parser.add_argument("command", choices=["status", "link", "unlink"])
     parser.add_argument("--group", "-g", metavar="GROUP")
+    parser.add_argument("--yes", "-y", action="store_true",
+                        help="Skip confirmation prompt (for non-interactive use)")
     args = parser.parse_args()
 
     if not args.group:
@@ -176,7 +181,7 @@ def main() -> None:
     elif args.command == "link":
         cmd_link(cfg, args.group)
     elif args.command == "unlink":
-        cmd_unlink(cfg, args.group)
+        cmd_unlink(cfg, args.group, yes=args.yes)
 
 
 if __name__ == "__main__":