fix: 手机保存图片使用 navigator.share 直接保存到相册

- 新增 composables/useSaveImage.js
  - saveImageFromUrl: data URL → 手机分享/桌面下载
  - captureAndSave: DOM元素 → html2canvas → 保存
  - saveCanvasImage: canvas → 保存
- RecipeDetailOverlay: saveImage 改用 saveImageFromUrl
- OilReference: saveModalImage 改用 captureAndSave
- 手机端调用 navigator.share({files}) 弹出系统分享面板

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

frontend/src/components/RecipeDetailOverlay.vue

@@ -583,11 +583,14 @@ async function saveImage() {
     await generateCardImage()
   }
   if (!cardImageUrl.value) return
-  const link = document.createElement('a')
-  link.download = `${recipe.value.name || '配方'}_配方卡.png`
-  link.href = cardImageUrl.value
-  link.click()
-  ui.showToast('已保存图片')
+  const filename = `${recipe.value.name || '配方'}_配方卡`
+  try {
+    const { saveImageFromUrl } = await import('../composables/useSaveImage')
+    await saveImageFromUrl(cardImageUrl.value, filename)
+    ui.showToast('已保存图片')
+  } catch {
+    ui.showToast('保存失败')
+  }
 }
 
 function copyText() {

frontend/src/composables/useSaveImage.js

@@ -0,0 +1,76 @@
+/**
+ * Save image — on mobile use native share (save to photos),
+ * on desktop trigger download.
+ */
+
+const isMobile = () => /iPhone|iPad|iPod|Android/i.test(navigator.userAgent)
+
+/**
+ * Save a data URL or blob as image.
+ * Mobile: navigator.share → save to photos
+ * Desktop: download link
+ */
+export async function saveImageFromUrl(dataUrl, filename) {
+  if (isMobile() && navigator.canShare) {
+    try {
+      const res = await fetch(dataUrl)
+      const blob = await res.blob()
+      const file = new File([blob], filename + '.png', { type: 'image/png' })
+      if (navigator.canShare({ files: [file] })) {
+        await navigator.share({ files: [file] })
+        return true
+      }
+    } catch {}
+  }
+  // Desktop fallback
+  const a = document.createElement('a')
+  a.href = dataUrl
+  a.download = filename + '.png'
+  a.click()
+  return true
+}
+
+/**
+ * Capture a DOM element as image and save it.
+ */
+export async function captureAndSave(element, filename) {
+  const { default: html2canvas } = await import('html2canvas')
+  // Hide buttons during capture
+  const buttons = element.querySelectorAll('button')
+  buttons.forEach(b => b.style.display = 'none')
+  try {
+    const canvas = await html2canvas(element, {
+      scale: 2,
+      backgroundColor: '#ffffff',
+      useCORS: true,
+    })
+    buttons.forEach(b => b.style.display = '')
+    return saveCanvasImage(canvas, filename)
+  } catch {
+    buttons.forEach(b => b.style.display = '')
+    return false
+  }
+}
+
+/**
+ * Save a canvas element as image.
+ */
+export async function saveCanvasImage(canvas, filename) {
+  if (isMobile() && navigator.canShare) {
+    try {
+      const blob = await new Promise(r => canvas.toBlob(r, 'image/png'))
+      const file = new File([blob], filename + '.png', { type: 'image/png' })
+      if (navigator.canShare({ files: [file] })) {
+        await navigator.share({ files: [file] })
+        return true
+      }
+    } catch {}
+  }
+  // Desktop fallback
+  const url = canvas.toDataURL('image/png')
+  const a = document.createElement('a')
+  a.href = url
+  a.download = filename + '.png'
+  a.click()
+  return true
+}

frontend/src/views/OilReference.vue

@@ -725,26 +725,18 @@ function exportPDF() {
   setTimeout(() => w.print(), 500)
 }
 
-// Save modal as image using html2canvas
+// Save modal as image (mobile: share to photos, desktop: download)
 async function saveModalImage(name) {
+  const overlay = document.querySelector('.modal-overlay')
+  if (!overlay) return
+  const cardEl = overlay.querySelector('[style*="border-radius: 20px"], [style*="border-radius:20px"]') ||
+                 overlay.querySelector('.oil-card-modal') || overlay.children[0]
+  if (!cardEl) return
   try {
-    const { default: html2canvas } = await import('html2canvas')
-    const overlay = document.querySelector('.modal-overlay')
-    if (!overlay) return
-    const cardEl = overlay.querySelector('[style*="border-radius: 20px"], [style*="border-radius:20px"]') || overlay.children[0]
-    if (!cardEl) return
-    // Hide close buttons during capture
-    const btns = cardEl.querySelectorAll('button')
-    btns.forEach(b => b.style.display = 'none')
-    const canvas = await html2canvas(cardEl, { scale: 2, backgroundColor: '#ffffff', useCORS: true })
-    btns.forEach(b => b.style.display = '')
-    const url = canvas.toDataURL('image/png')
-    const a = document.createElement('a')
-    a.href = url
-    a.download = (name || '精油知识卡') + '.png'
-    a.click()
-    ui.showToast('图片已保存')
-  } catch (e) {
+    const { captureAndSave } = await import('../composables/useSaveImage')
+    const ok = await captureAndSave(cardEl, name || '精油知识卡')
+    if (ok) ui.showToast('图片已保存')
+  } catch {
     ui.showToast('保存失败')
   }
 }