Fix Windows weblink handling: fullscreen Chrome, black overlay masking, proper process tree kill

Windows-specific fixes:
- _windows_play_weblink: uses --start-maximized + --app=URL for true fullscreen
- Shows black Win32 overlay before opening/closing Chrome to mask desktop
- _windows_kill_process_tree: uses taskkill /F /T to kill all Chrome child processes
- _Win32Overlay class: fullscreen borderless always-on-top black window
- Updated README to note Python 3.12 requirement and local data dir behavior

windows/README_WINDOWS_BUILD.md

@@ -36,7 +36,10 @@ The original app was built for **Raspberry Pi (Linux)**, using these technologie
 ## 🚀 Quick Start (Development)
 
 ### Prerequisites
-1. **Python 3.10+** (64-bit) — [python.org](https://python.org)
+1. **Python 3.12+** (64-bit) — [python.org](https://python.org)
+   - ⚠️ **Python 3.13+ is NOT supported** — Kivy 2.3.1 does not have pre-built wheels for it
+   - ⚠️ **Python 3.14 is NOT supported** — no Kivy wheels available
+   - ✅ **Python 3.12.9** is the recommended version (confirmed working)
 2. **FFmpeg** — for video codec support
    - Download from [ffmpeg.org](https://ffmpeg.org/download.html)
    - Add `bin\` folder to your PATH
@@ -46,8 +49,11 @@ The original app was built for **Raspberry Pi (Linux)**, using these technologie
 ```batch
 cd windows
 
-REM Create virtual environment
-python -m venv venv
+REM Create virtual environment with Python 3.12
+py -3.12 -m venv venv
+:: OR specify full path:
+:: "C:\Users\Dell-PC\AppData\Local\Programs\Python\Python312\python.exe" -m venv venv
+
 venv\Scripts\activate
 
 REM Install dependencies
@@ -86,8 +92,10 @@ For a **single-file .exe**, edit `build.spec` — uncomment the `exe_onefile` se
 
 ## ⚙️ Configuration
 
-1. On first run, config files are created in `%APPDATA%\KiwySignage\`
-2. Edit `%APPDATA%\KiwySignage\config\app_config.json` to set your server:
+1. On first run, config files are created in the **same folder as the executable** (not in `%APPDATA%`)
+   - The .exe creates: `config/`, `media/`, `playlists/`, `logs/` directories locally
+   - This allows you to copy the entire `dist\KiwySignagePlayer\` folder anywhere and it works
+2. Edit `config\app_config.json` (next to the .exe) to set your server:
 
 ```json
 {