feat(theme): add environment variable support for theme selection

- Add BOILERPLATE_THEME environment variable to control theme selection dynamically
- Implement automatic theme validation with fallback to default theme
- Update theme configuration to support environment-based theme switching
- Document environment variable method as recommended approach for theme changes
- Enhance documentation with complete setup instructions and validation details

Author: Sébastien HEYD

docs/docs/8.x/configuration/theme.md

@@ -6,7 +6,17 @@ The `config/boilerplate/theme.php` file allows to define the backend theme param
 
 ```php
 <?php
-$theme = include __DIR__.'/themes/default.php';
+// Selected theme
+$selectedTheme = env('BOILERPLATE_THEME', 'default');
+
+// Check if theme exists
+$themePath = __DIR__.'/themes/'.$selectedTheme.'.php';
+if (!file_exists($themePath)) {
+    $selectedTheme = 'default';
+    $themePath = __DIR__.'/themes/default.php';
+}
+
+$theme = include $themePath;
 
 $theme += [
     'navbar' => [               // Additionnal views to append items to the navbar
@@ -24,7 +34,9 @@ return $theme;
 
 ## theme
 
-Theme to use.
+Theme to use. You can change the theme by setting the `BOILERPLATE_THEME` environment variable in your `.env` file.
+
+The system automatically validates that the specified theme file exists and falls back to the default theme if not found.
 
 See [How to change theme](/howto/change-theme)
 

docs/docs/8.x/howto/change_theme.md

@@ -1,14 +1,34 @@
 # Change theme
 
-To change the theme, you must define it in the [`config/theme.php`](/configuration/theme) file.
+To change the theme, you can use the `BOILERPLATE_THEME` environment variable in your `.env` file or define it directly in the [`config/theme.php`](/configuration/theme) file.
 
-All you have to do is to include the theme file you want to use :
+## Method 1: Environment Variable (Recommended)
+
+Add the theme name to your `.env` file:
+
+```env
+BOILERPLATE_THEME=black
+```
+
+## Method 2: Direct Configuration
+
+You can also manually modify the theme in your `config/boilerplate/theme.php` file:
 
 ```php
-$theme = include __DIR__.'/themes/default.php';
+// Selected theme
+$selectedTheme = env('BOILERPLATE_THEME', 'red'); // Change default here
+
+// Check if theme exists
+$themePath = __DIR__.'/themes/'.$selectedTheme.'.php';
+if (!file_exists($themePath)) {
+    $selectedTheme = 'default';
+    $themePath = __DIR__.'/themes/default.php';
+}
+
+$theme = include $themePath;
 ```
 
-> Available themes are `default`, `black`, `red`.
+> Available themes are `default`, `black`, `red`. The system automatically validates theme existence and falls back to default if the specified theme is not found.
 
 <a :href="$withBase('/assets/img/logs_stats.png')" class="img-link"><img :src="$withBase('/assets/img/logs_stats.png')" style="max-width:100%;height:100px;margin-right:.5rem" /></a>
 <a :href="$withBase('/assets/img/theme_black.png')" class="img-link"><img :src="$withBase('/assets/img/theme_black.png')" style="max-width:100%;height:100px;margin-right:.5rem" /></a>
@@ -18,11 +38,19 @@ $theme = include __DIR__.'/themes/default.php';
 
 ## Create a new theme
 
-You don't have to create a new theme, you can also edit the `default` theme. But it is recommanded to create a new theme, so you can add modifications without touching the default themes.
+You don't have to create a new theme, you can also edit the `default` theme. But it is recommended to create a new theme, so you can add modifications without touching the default themes.
+
+To create a new theme:
 
-To create a new theme, just copy the `default.php` file in the `config` folder to a new theme file. 
+1. Copy the `default.php` file in the `config/boilerplate/themes/` folder to a new theme file (e.g., `custom.php`)
+2. Modify your new theme file as needed  
+3. Set the `BOILERPLATE_THEME` environment variable to your new theme name:
+
+```env
+BOILERPLATE_THEME=custom
+```
 
-After that, just modify the theme included in `config/theme.php` by calling your new theme file.
+The system will automatically load your custom theme. If the theme file doesn't exist, it will fallback to the default theme.
 
 ---
 

src/config/theme.php

@@ -1,6 +1,16 @@
 <?php
 
-$theme = include __DIR__.'/themes/default.php';
+// Selected theme
+$selectedTheme = env('BOILERPLATE_THEME', 'default');
+
+// Check if theme exists
+$themePath = __DIR__.'/themes/'.$selectedTheme.'.php';
+if (!file_exists($themePath)) {
+    $selectedTheme = 'default';
+    $themePath = __DIR__.'/themes/default.php';
+}
+
+$theme = include $themePath;
 
 $theme += [
     'navbar' => [               // Additionnal views to append items to the navbar