feat: implement reactive EditorPanel with bidirectional sync

- Reorganize editor components into dedicated folder
- Create PageSettings component with page format, margins, background controls
- Create TextSettings component (structure only, to be populated)
- Implement debounced updates (1s delay) to stylesheet store
- Add bidirectional sync between EditorPanel and StylesheetViewer
- Preserve scroll position as percentage when reloading preview
- Move @page rules from App.vue to stylesheet.css for unified management
- Extend css-parsing utils to handle text values (e.g., 'A4', 'portrait')
- Remove unnecessary comments, use explicit naming instead

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

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

src/components/editor/EditorPanel.vue

@@ -0,0 +1,84 @@
+<template>
+  <aside id="editor-panel">
+    <nav class="tabs">
+      <button
+        type="button"
+        :class="{ active: activeTab === 'document' }"
+        @click="activeTab = 'document'"
+      >
+        Document
+      </button>
+      <button
+        type="button"
+        :class="{ active: activeTab === 'code' }"
+        @click="activeTab = 'code'"
+      >
+        Code
+      </button>
+      <button
+        type="button"
+        :class="{ active: activeTab === 'contenu' }"
+        @click="activeTab = 'contenu'"
+      >
+        Contenu
+      </button>
+    </nav>
+
+    <div class="tab-content">
+      <div v-if="activeTab === 'document'" class="tab-panel">
+        <PageSettings />
+        <TextSettings />
+      </div>
+
+      <div v-else-if="activeTab === 'code'" class="tab-panel">
+        <!-- Code tab content -->
+      </div>
+
+      <div v-else-if="activeTab === 'contenu'" class="tab-panel">
+        <!-- Contenu tab content -->
+      </div>
+    </div>
+  </aside>
+</template>
+
+<script setup>
+import { ref } from 'vue';
+import PageSettings from './PageSettings.vue';
+import TextSettings from './TextSettings.vue';
+
+// Tab management
+const activeTab = ref('document');
+</script>
+
+<style scoped>
+#editor-panel {
+  position: fixed;
+  top: 0;
+  left: 0;
+  width: 250px;
+  height: 100vh;
+  background: #f5f5f5;
+  padding: 1rem;
+  box-shadow: 2px 0 8px rgba(0, 0, 0, 0.1);
+  overflow-y: auto;
+}
+
+h3 {
+  margin-top: 0;
+}
+
+.control {
+  margin-bottom: 1rem;
+}
+
+.control label {
+  display: block;
+  margin-bottom: 0.25rem;
+  font-size: 0.875rem;
+}
+
+.control input {
+  width: 80px;
+  padding: 0.25rem;
+}
+</style>