fix: 保存图片一次点击即弹分享面板

根因: navigator.share 需要在用户手势同步上下文中调用。
之前点保存→html2canvas截图(异步)→share(手势已过期)，失败。

修复: 打开 modal 时预生成图片(watch showDilution/showContra,
openOilDetail里预生成)，点保存按钮时 dataUrl 已缓存，
navigator.share 在用户手势上下文内直接调用，一次即弹分享面板。

保存按钮放回卡片内部。

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/OilReference.vue

@@ -36,9 +36,11 @@
           <div style="margin-top:16px;padding:12px;background:#e8f5e9;border-radius:10px;font-size:12px;color:#2e7d32;text-align:center">
             💡 稀释比例 = 1滴精油 : N滴椰子油<br>比例越大越温和，新手建议从高稀释比例开始
           </div>
+          <div style="text-align:center;margin-top:12px">
+            <button @click="saveDilutionImage" style="padding:8px 16px;border-radius:10px;border:1.5px solid var(--sage);background:white;color:var(--sage-dark);cursor:pointer;font-size:13px;font-family:inherit">💾 保存图片</button>
+          </div>
         </div>
       </div>
-      <button @click="saveDilutionImage" style="margin-top:12px;padding:8px 20px;border-radius:20px;border:none;background:rgba(255,255,255,0.9);color:#2e7d32;cursor:pointer;font-size:13px;font-family:inherit;font-weight:600;z-index:2">💾 保存图片</button>
     </div>
 
     <!-- Safety Cautions Modal -->
@@ -75,9 +77,11 @@
             <span style="font-size:20px;flex-shrink:0">💧</span>
             <div><div style="font-weight:600;color:var(--text-dark)">少量多次，多喝水</div><div style="font-size:12px;color:var(--text-light);margin-top:2px">使用精油后多补充水分，帮助身体代谢</div></div>
           </div>
+          <div style="text-align:center;margin-top:12px">
+            <button @click="saveContraImage" style="padding:8px 16px;border-radius:10px;border:1.5px solid #e65100;background:white;color:#e65100;cursor:pointer;font-size:13px;font-family:inherit">💾 保存图片</button>
+          </div>
         </div>
       </div>
-      <button @click="saveContraImage" style="margin-top:12px;padding:8px 20px;border-radius:20px;border:none;background:rgba(255,255,255,0.9);color:#e65100;cursor:pointer;font-size:13px;font-family:inherit;font-weight:600;z-index:2">💾 保存图片</button>
     </div>
 
     <!-- Search + View Toggle + Add + PDF -->
@@ -203,9 +207,11 @@
             <h4 class="oil-card-caution-title">⚠️ 注意事项</h4>
             <p>{{ activeCard.caution }}</p>
           </div>
+          <div style="text-align:center;padding-top:12px">
+            <button class="btn btn-outline btn-sm" @click="saveCardImage(activeCardName)">💾 保存图片</button>
+          </div>
         </div>
       </div>
-      <button @click="saveCardImage(activeCardName)" style="margin-top:12px;padding:8px 20px;border-radius:20px;border:none;background:rgba(255,255,255,0.9);color:var(--sage-dark);cursor:pointer;font-size:13px;font-family:inherit;font-weight:600;z-index:2">💾 保存图片</button>
     </div>
 
     <!-- Simple Oil Detail Panel (for oils without a knowledge card) -->
@@ -546,12 +552,18 @@ function parseMethodBadges(methodStr) {
 }
 
 // Actions
-function openOilDetail(name) {
+async function openOilDetail(name) {
   const card = getOilCard(name)
   if (card) {
     activeCardName.value = name
     activeCard.value = card
     selectedOilName.value = null
+    // Pre-generate card image for instant save
+    oilCardImageUrl.value = null
+    await nextTick()
+    await new Promise(r => setTimeout(r, 300))
+    const el = document.querySelector('.oil-card-modal')
+    if (el) await generateImageFromRef({ value: el }, oilCardImageUrl)
   } else {
     activeCard.value = null
     activeCardName.value = null
@@ -748,33 +760,59 @@ async function generateImageFromRef(elRef, imageUrlRef) {
   }
 }
 
-async function saveGeneratedImage(imageUrlRef, elRef, name) {
-  // Generate if not already done
-  if (!imageUrlRef.value) {
-    await generateImageFromRef(elRef, imageUrlRef)
+// When modal opens, pre-generate the image (so save button has instant dataUrl)
+watch(showDilution, async (v) => {
+  if (v) {
+    dilutionImageUrl.value = null
+    await nextTick()
+    await new Promise(r => setTimeout(r, 300))
+    await generateImageFromRef(dilutionCardRef, dilutionImageUrl)
   }
-  if (!imageUrlRef.value) {
-    ui.showToast('图片生成失败')
+})
+watch(showContra, async (v) => {
+  if (v) {
+    contraImageUrl.value = null
+    await nextTick()
+    await new Promise(r => setTimeout(r, 300))
+    await generateImageFromRef(contraCardRef, contraImageUrl)
+  }
+})
+
+// Save: dataUrl is already cached, navigator.share runs in fresh user gesture
+async function saveDilutionImage() {
+  if (!dilutionImageUrl.value) {
+    ui.showToast('图片生成中，请稍后再试')
     return
   }
-  // Same as RecipeDetailOverlay.saveImage
   const { saveImageFromUrl } = await import('../composables/useSaveImage')
-  await saveImageFromUrl(imageUrlRef.value, name)
+  await saveImageFromUrl(dilutionImageUrl.value, '精油稀释比例指南')
   ui.showToast('已保存图片')
 }
 
-function saveDilutionImage() {
-  saveGeneratedImage(dilutionImageUrl, dilutionCardRef, '精油稀释比例指南')
+async function saveContraImage() {
+  if (!contraImageUrl.value) {
+    ui.showToast('图片生成中，请稍后再试')
+    return
+  }
+  const { saveImageFromUrl } = await import('../composables/useSaveImage')
+  await saveImageFromUrl(contraImageUrl.value, '精油使用禁忌')
+  ui.showToast('已保存图片')
 }
-function saveContraImage() {
-  saveGeneratedImage(contraImageUrl, contraCardRef, '精油使用禁忌')
-}
-function saveCardImage(name) {
+
+async function saveCardImage(name) {
+  // Oil card: generate on demand since we don't know which card opens
   const el = document.querySelector('.oil-card-modal')
   if (!el) { ui.showToast('找不到卡片'); return }
-  // Use a temporary ref-like object
-  const tmpRef = { value: el }
-  saveGeneratedImage(oilCardImageUrl, tmpRef, name + '_精油知识卡')
+  if (!oilCardImageUrl.value) {
+    await generateImageFromRef({ value: el }, oilCardImageUrl)
+  }
+  if (!oilCardImageUrl.value) {
+    ui.showToast('图片生成失败')
+    return
+  }
+  const { saveImageFromUrl } = await import('../composables/useSaveImage')
+  await saveImageFromUrl(oilCardImageUrl.value, name + '_精油知识卡')
+  ui.showToast('已保存图片')
 }
 </script>