feat: AI cost tracking, pre-launch balance check, low balance alerts

- store/ai_charge.go: local AI cost tracking per call (SQLite)
- wallet/usdc.go: shared USDC balance query (Base chain RPC)
- Pre-launch: estimate daily cost + runway days
- Low balance: warn <$1, error at $0 (every 10 cycles)
- API: GET /api/ai-costs for cost history
- Frontend: model cards show price per call
- Frontend: wallet create + QR deposit + balance display

web/package-lock.json

@@ -18,6 +18,7 @@
         "katex": "^0.16.27",
         "lightweight-charts": "^5.1.0",
         "lucide-react": "^0.552.0",
+        "qrcode.react": "^4.2.0",
         "react": "^18.3.1",
         "react-dom": "^18.3.1",
         "react-password-checklist": "^1.8.1",
@@ -6837,6 +6838,15 @@
         "node": ">=6"
       }
     },
+    "node_modules/qrcode.react": {
+      "version": "4.2.0",
+      "resolved": "https://registry.npmjs.org/qrcode.react/-/qrcode.react-4.2.0.tgz",
+      "integrity": "sha512-QpgqWi8rD9DsS9EP3z7BT+5lY5SFhsqGjpgW5DY/i3mK4M9DTBNz3ErMi8BWYEfI3L0d8GIbGmcdFAS1uIRGjA==",
+      "license": "ISC",
+      "peerDependencies": {
+        "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0"
+      }
+    },
     "node_modules/queue-microtask": {
       "version": "1.2.3",
       "resolved": "https://registry.npmjs.org/queue-microtask/-/queue-microtask-1.2.3.tgz",