fix: complete remaining 8 optimization items

- HTTP connection pooling: UpstreamClient & WebsiteClient reuse httpx.Client
- Deduplicate decimal_string into shared app/utils/number.py
- Split scheduler transaction: snapshot write → webhook/website sync in separate sessions
- Remove hardcoded 170.106.100.210 migration from database.py
- Reset consecutive_failures on upstream update
- Healthcheck: install curl, replace python -c with curl -f
- Add .dockerignore to reduce build context
- Frontend: add axios-retry with exponential backoff (5xx/network errors only)

frontend/package-lock.json

@@ -10,6 +10,7 @@
       "dependencies": {
         "@element-plus/icons-vue": "^2.3.1",
         "axios": "^1.7.9",
+        "axios-retry": "^4.5.0",
         "dayjs": "^1.11.13",
         "element-plus": "^2.8.8",
         "pinia": "^2.2.6",
@@ -1202,6 +1203,18 @@
         "proxy-from-env": "^2.1.0"
       }
     },
+    "node_modules/axios-retry": {
+      "version": "4.5.0",
+      "resolved": "https://registry.npmmirror.com/axios-retry/-/axios-retry-4.5.0.tgz",
+      "integrity": "sha512-aR99oXhpEDGo0UuAlYcn2iGRds30k366Zfa05XWScR9QaQD4JYiP3/1Qt1u7YlefUOK+cn0CcwoL1oefavQUlQ==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "is-retry-allowed": "^2.2.0"
+      },
+      "peerDependencies": {
+        "axios": "0.x || 1.x"
+      }
+    },
     "node_modules/balanced-match": {
       "version": "1.0.2",
       "resolved": "https://registry.npmmirror.com/balanced-match/-/balanced-match-1.0.2.tgz",
@@ -1593,6 +1606,18 @@
         "he": "bin/he"
       }
     },
+    "node_modules/is-retry-allowed": {
+      "version": "2.2.0",
+      "resolved": "https://registry.npmmirror.com/is-retry-allowed/-/is-retry-allowed-2.2.0.tgz",
+      "integrity": "sha512-XVm7LOeLpTW4jV19QSH38vkswxoLud8sQ57YwJVTPWdiaI9I8keEhGFpBlslyVsgdQy4Opg8QOLb8YRgsyZiQg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=10"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/sindresorhus"
+      }
+    },
     "node_modules/lodash": {
       "version": "4.18.1",
       "resolved": "https://registry.npmmirror.com/lodash/-/lodash-4.18.1.tgz",