feat: integrate Coloris color picker for background field

Add Coloris.js library for enhanced color selection in PageSettings with
automatic button state sync across tab changes.

Features:
- Color picker with swatches, alpha support, and format toggle (hex/rgb/hsl)
- Button positioned to the left of input field
- Automatic sync when switching tabs (remembers selected color)
- Close button and click-outside-to-close functionality
- Dark theme with pill UI style

Changes:
- Install @melloware/coloris package
- PageSettings.vue: Integrate Coloris with data-coloris attribute,
  add tab visibility detection via provide/inject, force button update
  when returning to document tab
- EditorPanel.vue: Provide activeTab to child components, increase
  panel width to 30rem
- _forms.scss: Add .input-with-color styles with custom Coloris
  button positioning (absolute positioned to left of input)
- Temporarily comment out rgb/hex format buttons (replaced by Coloris
  format toggle)

Technical details:
- Uses provide/inject pattern to detect tab changes
- Triggers synthetic input events to force Coloris button refresh
- Custom CSS overrides to position swatch button correctly

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/components/editor/PageSettings.vue

@@ -18,12 +18,24 @@
     <div class="settings-subsection">
       <div class="field field--view-only">
         <label for="page-width">Largeur</label>
-        <input id="page-width" type="text" :value="pageWidth" disabled />
+        <input
+          id="page-width"
+          type="number"
+          :value="parseInt(pageWidth)"
+          disabled
+        />
+        <button type="button" disabled>mm</button>
       </div>
 
       <div class="field field--view-only">
         <label for="page-height">Hauteur</label>
-        <input id="page-height" type="text" :value="pageHeight" disabled />
+        <input
+          id="page-height"
+          type="number"
+          :value="parseInt(pageHeight)"
+          disabled
+        />
+        <button type="button" disabled>mm</button>
       </div>
     </div>
 
@@ -146,8 +158,15 @@
     <div class="settings-subsection">
       <div class="field">
         <label for="background">Arrière-plan</label>
-        <div class="input-with-unit">
-          <input id="background" type="text" v-model="background.value" />
+        <div class="input-with-color">
+          <input
+            ref="backgroundColorInput"
+            type="text"
+            id="background"
+            v-model="background.value"
+            data-coloris
+          />
+          <!-- Temporarily commented out
           <div class="unit-toggle">
             <button
               type="button"
@@ -164,6 +183,7 @@
               hex
             </button>
           </div>
+          -->
         </div>
       </div>
     </div>
@@ -195,10 +215,14 @@
 </template>
 
 <script setup>
-import { ref, computed, watch, onMounted } from 'vue';
+import { ref, computed, watch, onMounted, inject } from 'vue';
 import { useStylesheetStore } from '../../stores/stylesheet';
+import Coloris from '@melloware/coloris';
+import '@melloware/coloris/dist/coloris.css';
 
 const stylesheetStore = useStylesheetStore();
+const backgroundColorInput = ref(null);
+const activeTab = inject('activeTab', ref('document'));
 
 let isUpdatingFromStore = false;
 let updateTimer = null;
@@ -411,7 +435,58 @@ watch(
   }
 );
 
+const updateColorisButton = () => {
+  const input = backgroundColorInput.value;
+  if (input && background.value.value) {
+    // Force Coloris to update by triggering a change event
+    const event = new Event('input', { bubbles: true });
+    input.dispatchEvent(event);
+  }
+};
+
+// Watch for when the user returns to the "document" tab
+watch(activeTab, (newTab, oldTab) => {
+  if (newTab === 'document' && oldTab !== 'document' && background.value.value) {
+    // Small delay to ensure DOM is ready
+    setTimeout(updateColorisButton, 100);
+  }
+});
+
 onMounted(() => {
   syncFromStore();
+
+  // Initialize Coloris
+  Coloris.init();
+  Coloris({
+    el: '[data-coloris]',
+    theme: 'pill',
+    themeMode: 'dark',
+    formatToggle: true,
+    alpha: true,
+    closeButton: true,
+    closeLabel: 'Fermer',
+    clearButton: true,
+    clearLabel: 'Effacer',
+    swatchesOnly: false,
+    inline: false,
+    wrap: true,
+    swatches: [
+      '#264653',
+      '#2a9d8f',
+      '#e9c46a',
+      '#f4a261',
+      '#e76f51',
+      '#d62828',
+      '#023e8a',
+      '#0077b6',
+      '#ffffff',
+      '#000000',
+    ],
+  });
+
+  // Initialize button color if value exists
+  if (background.value.value) {
+    setTimeout(updateColorisButton, 100);
+  }
 });
 </script>