fix: Fix trading precision issues and improve error handling

- Fix quantity precision calculation for Binance, OKX, Bybit, Bitget, Deepcoin exchanges
- Improve OpenRouter API error handling with detailed error messages
- Add SECRET_KEY validation in Docker deployment entrypoint
- Fix K-line chart measurement tool click issue
- Adapt billing page text colors for dark theme
- Update frontend build files

scripts/generate-secret-key.ps1

@@ -0,0 +1,31 @@
+# Helper script to generate a secure SECRET_KEY for QuantDinger (Windows PowerShell)
+# Usage: .\scripts\generate-secret-key.ps1
+
+$envFile = "backend_api_python\.env"
+
+# Check if .env exists
+if (-not (Test-Path $envFile)) {
+    Write-Host "Error: $envFile not found" -ForegroundColor Red
+    Write-Host "Please run: Copy-Item backend_api_python\env.example -Destination backend_api_python\.env"
+    exit 1
+}
+
+# Generate a secure random key
+$newKey = python -c "import secrets; print(secrets.token_hex(32))"
+
+if ($LASTEXITCODE -ne 0) {
+    Write-Host "Error: Failed to generate SECRET_KEY. Make sure Python is installed." -ForegroundColor Red
+    exit 1
+}
+
+# Update SECRET_KEY in .env file
+$content = Get-Content $envFile
+$content = $content -replace '^SECRET_KEY=.*', "SECRET_KEY=$newKey"
+$content | Set-Content $envFile
+
+Write-Host "✅ SECRET_KEY generated and updated in $envFile" -ForegroundColor Green
+Write-Host ""
+Write-Host "Generated key: $newKey" -ForegroundColor Cyan
+Write-Host ""
+Write-Host "You can now start the application:"
+Write-Host "  docker-compose up -d --build"