Add CSV upload panel for meters and readings

- Add CSV upload service with upsert logic for meters
- Add CSV upload routes (POST /csv-upload/meters, POST /csv-upload/readings)
- Add template download endpoints for CSV format
- Create standalone upload-panel React app on port 5174
- Support concentrator_serial lookup for meter creation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

upload-panel/tsconfig.node.json

@@ -0,0 +1,11 @@
+{
+  "compilerOptions": {
+    "composite": true,
+    "skipLibCheck": true,
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "allowSyntheticDefaultImports": true,
+    "strict": true
+  },
+  "include": ["vite.config.ts"]
+}