feat: responsive images for investigation template

Add srcsets in config:
- cover-hero: 940px fixe ≥1000px, 90vw en dessous
- body-full: 100vw (1 colonne)
- body-half: 50vw ≥768px, 90vw en dessous (2 colonnes)

Apply in templates/snippets:
- Cover hero → snippet picture + cover-hero
- Body 1-col images → snippet picture + body-full
- Body 2-col images → snippet picture + body-half
- gallery.php → snippet picture (sizes/srcset paramétrables)
- beforeafter.php → srcset/sizes sur <img> (pas de <picture> pour ne pas
  casser le JS du slider)

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

site/config/config.php

@@ -32,6 +32,31 @@ return [
         '1000w' => ['width' => 1000, 'format' => 'webp'],
         '1456w' => ['width' => 1456, 'format' => 'webp'],
       ],
+      // Hero cover investigation : 940px fixe ≥1000px, 90vw en dessous
+      'cover-hero' => [680, 940, 1200, 1880],
+      'cover-hero-webp' => [
+        '680w'  => ['width' => 680,  'format' => 'webp'],
+        '940w'  => ['width' => 940,  'format' => 'webp'],
+        '1200w' => ['width' => 1200, 'format' => 'webp'],
+        '1880w' => ['width' => 1880, 'format' => 'webp'],
+      ],
+      // Body 1 colonne : 100vw
+      'body-full' => [750, 1000, 1440, 1880],
+      'body-full-webp' => [
+        '750w'  => ['width' => 750,  'format' => 'webp'],
+        '1000w' => ['width' => 1000, 'format' => 'webp'],
+        '1440w' => ['width' => 1440, 'format' => 'webp'],
+        '1880w' => ['width' => 1880, 'format' => 'webp'],
+      ],
+      // Body 2 colonnes : 50vw ≥768px, 90vw en dessous
+      'body-half' => [680, 720, 1000, 1380, 1440],
+      'body-half-webp' => [
+        '680w'  => ['width' => 680,  'format' => 'webp'],
+        '720w'  => ['width' => 720,  'format' => 'webp'],
+        '1000w' => ['width' => 1000, 'format' => 'webp'],
+        '1380w' => ['width' => 1380, 'format' => 'webp'],
+        '1440w' => ['width' => 1440, 'format' => 'webp'],
+      ],
     ],
   ],
   'panel' => [