fix: 支持HEIC格式上传 + 压缩目标调小

- HEIC/HEIF格式自动转换为JPEG后压缩
- 压缩目标调小确保不超后端限制（QR/logo 300KB，背景 600KB）

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

frontend/package-lock.json

@@ -9,6 +9,7 @@
       "version": "0.0.0",
       "dependencies": {
         "exceljs": "^4.4.0",
+        "heic2any": "^0.0.4",
         "html2canvas": "^1.4.1",
         "pinia": "^2.3.1",
         "vue": "^3.5.32",
@@ -2871,6 +2872,12 @@
         "node": ">= 0.4"
       }
     },
+    "node_modules/heic2any": {
+      "version": "0.0.4",
+      "resolved": "https://registry.npmjs.org/heic2any/-/heic2any-0.0.4.tgz",
+      "integrity": "sha512-3lLnZiDELfabVH87htnRolZ2iehX9zwpRyGNz22GKXIu0fznlblf0/ftppXKNqS26dqFSeqfIBhAmAj/uSp0cA==",
+      "license": "MIT"
+    },
     "node_modules/html-encoding-sniffer": {
       "version": "6.0.0",
       "resolved": "https://registry.npmjs.org/html-encoding-sniffer/-/html-encoding-sniffer-6.0.0.tgz",