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>

README.md

@@ -21,6 +21,7 @@ Python toolchain for managing Arma 3 mod presets: parse launcher exports, compar
    - [update_mods.py](#update_modspy)
    - [check_names.py](#check_namespy)
    - [run.py](#runpy)
+   - [gui.py](#guipy)
 6. [Migrating Existing Mods](#migrating-existing-mods)
 7. [Folder Structure](#folder-structure)
 8. [Moving to a New Device](#moving-to-a-new-device)
@@ -35,6 +36,7 @@ Python toolchain for managing Arma 3 mod presets: parse launcher exports, compar
 | Python | >= 3.9 | `python --version` |
 | requests | any | `pip install requests` |
 | tqdm | any | `pip install tqdm` |
+| customtkinter | any | `pip install customtkinter` (GUI only) |
 | Windows or Linux | — | Windows uses junctions, Linux uses symlinks |
 
 Run the dep checker to confirm everything is ready:
@@ -472,6 +474,30 @@ Orchestrator that chains all four pipeline steps. Described in [Quick Start](#qu
 
 ---
 
+### gui.py
+
+Launch the graphical interface for the toolchain.
+
+```bash
+python gui.py
+```
+
+Opens a CustomTkinter desktop window with a sidebar navigation and the following views:
+
+| View | Purpose |
+|------|---------|
+| Dashboard | Overview: status, quick stats, recent activity |
+| Mods | Browse and manage downloaded mods by group |
+| Tools | Link/unlink, rename, sync missing, check server |
+| Logs | Real-time log output from pipeline operations |
+| Settings | Edit `config.json` (server URL, paths, credentials) |
+
+On first launch (no `config.json`), a setup wizard walks you through creating one.
+
+**Requires:** `customtkinter` (`pip install customtkinter`).
+
+---
+
 ## Migrating Existing Mods
 
 If the Arma 3 Server already has mods installed and you want to bring them under this toolchain without re-downloading:
@@ -520,6 +546,19 @@ arma-modlist-tools/
 |   |- config.py              # config.json loader
 |   |- compat.py              # OS detection + encoding fix
 |
+|- gui/                       # GUI package (CustomTkinter desktop app)
+|   |- __init__.py            # Theme setup + run_app() entry point
+|   |- app.py                 # Main window, view management, pipeline runner
+|   |- wizard.py              # First-run config setup wizard
+|   |- _constants.py          # Window size, color, path constants
+|   |- _io.py                 # stdout/stderr → thread-safe queue for live logs
+|   |- views/
+|       |- dashboard.py       # Overview view
+|       |- mods.py            # Mod browser view
+|       |- tools.py           # Tool actions view
+|       |- logs.py            # Real-time log view
+|       |- settings.py        # Config editor view
+|
 |- modlist_html/              # INPUT: put your .html preset exports here
 |   |- MyPreset_A.html
 |   |- MyPreset_B.html
@@ -540,7 +579,9 @@ arma-modlist-tools/
 |- config.json                # YOUR config (gitignored — contains credentials)
 |- config.template.json       # Template to copy from
 |- requirements.txt
+|- selection.json             # GUI selection state (persisted between sessions)
 |
+|- gui.py                     # GUI entry point
 |- run.py                     # Orchestrator (parse + compare + fetch + link)
 |- parse_modlist.py           # Step 1 standalone
 |- compare_modlists.py        # Step 2 standalone