feat: add page template interaction with PagePopup

Implements page edge hover detection and click handling:
- Hover near page edges (30px threshold) shows light outline
- Click on page edge opens PagePopup for template customization
- PagePopup component similar to ElementPopup but for @page rules
- Both popups coordinate to show only one at a time

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

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

src/components/PagePopup.vue

@@ -0,0 +1,163 @@
+<template>
+  <div
+    v-if="visible"
+    id="page-popup"
+    :style="{ top: position.y + 'px', left: position.x + 'px' }"
+  >
+    <div class="popup-header">
+      <span>{{ pageSelector }}</span>
+      <button class="close-btn" @click="close">×</button>
+    </div>
+    <div class="popup-body">
+      <div class="popup-controls">
+        <p class="info">Gabarit de page</p>
+        <!-- Additional page-specific controls will be added here later -->
+      </div>
+      <div class="popup-css">
+        <textarea
+          :value="pageCss"
+          @input="handleCssInput"
+          spellcheck="false"
+        ></textarea>
+      </div>
+    </div>
+  </div>
+</template>
+
+<script setup>
+import { ref, computed } from 'vue';
+import { useStylesheetStore } from '../stores/stylesheet';
+
+const stylesheetStore = useStylesheetStore();
+
+const props = defineProps({
+  iframeRef: Object,
+});
+
+const visible = ref(false);
+const position = ref({ x: 0, y: 0 });
+const pageSelector = ref('@page');
+const selectedPageElement = ref(null);
+
+const calculatePosition = (pageElement) => {
+  const rect = pageElement.getBoundingClientRect();
+  const iframeRect = props.iframeRef.getBoundingClientRect();
+  return {
+    x: iframeRect.left + rect.left + 20,
+    y: iframeRect.top + rect.top + 20,
+  };
+};
+
+const open = (pageElement) => {
+  selectedPageElement.value = pageElement;
+  pageSelector.value = '@page';
+  position.value = calculatePosition(pageElement);
+
+  // Add border to the selected page
+  pageElement.style.outline = '2px solid #61afef';
+
+  visible.value = true;
+};
+
+const close = () => {
+  // Remove border from the selected page
+  if (selectedPageElement.value) {
+    selectedPageElement.value.style.outline = '';
+    selectedPageElement.value = null;
+  }
+  visible.value = false;
+};
+
+const pageCss = computed(() => {
+  return stylesheetStore.extractBlock('@page') || '';
+});
+
+let cssDebounceTimer = null;
+
+const handleCssInput = (event) => {
+  const newCss = event.target.value;
+
+  if (cssDebounceTimer) {
+    clearTimeout(cssDebounceTimer);
+  }
+
+  cssDebounceTimer = setTimeout(() => {
+    const oldBlock = pageCss.value;
+    if (oldBlock) {
+      stylesheetStore.content = stylesheetStore.content.replace(oldBlock, newCss);
+    }
+  }, 500);
+};
+
+defineExpose({ open, close, visible });
+</script>
+
+<style scoped>
+#page-popup {
+  position: fixed;
+  background: white;
+  border-radius: 4px;
+  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
+  z-index: 10000;
+  min-width: 400px;
+  max-width: 500px;
+}
+
+.popup-header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: 0.5rem 0.75rem;
+  border-bottom: 1px solid #eee;
+  font-size: 0.875rem;
+  font-weight: bold;
+  background: #f5f5f5;
+}
+
+.close-btn {
+  background: none;
+  border: none;
+  cursor: pointer;
+  font-size: 1.25rem;
+  line-height: 1;
+  padding: 0;
+}
+
+.popup-body {
+  display: flex;
+  gap: 1px;
+  background: #eee;
+}
+
+.popup-controls {
+  flex: 1;
+  padding: 0.75rem;
+  background: white;
+}
+
+.popup-css {
+  flex: 1;
+  background: #1e1e1e;
+  display: flex;
+}
+
+.popup-css textarea {
+  width: 100%;
+  height: 200px;
+  background: #1e1e1e;
+  color: #abb2bf;
+  border: none;
+  padding: 0.75rem;
+  font-family: 'Courier New', Courier, monospace;
+  font-size: 0.75rem;
+  line-height: 1.4;
+  resize: none;
+  outline: none;
+}
+
+.info {
+  font-size: 0.875rem;
+  color: #666;
+  margin: 0 0 0.5rem 0;
+}
+</style>