fix: require production database connection environment

src/dotnet/QuantEngine.Web/Program.cs

@@ -81,6 +81,12 @@ try
     // PostgreSQL Dapper Setup
     var connectionString = builder.Configuration.GetConnectionString("DefaultConnection")
         ?? throw new InvalidOperationException("Connection string 'DefaultConnection' is required.");
+    if (builder.Environment.IsProduction()
+        && string.IsNullOrWhiteSpace(Environment.GetEnvironmentVariable("ConnectionStrings__DefaultConnection")))
+    {
+        throw new InvalidOperationException(
+            "Production requires ConnectionStrings__DefaultConnection from the service environment.");
+    }
 
     var configuredDatabase = new NpgsqlConnectionStringBuilder(connectionString).Database;
     if (!string.Equals(configuredDatabase, "quantenginedb", StringComparison.OrdinalIgnoreCase))

src/dotnet/QuantEngine.Web/appsettings.Development.json

@@ -6,7 +6,7 @@
     }
   },
   "ConnectionStrings": {
-    "DefaultConnection": "Host=127.0.0.1;Database=quantenginedb;Username=quantengine_app;Password=quantengine_app;Search Path=quantengine;"
+    "DefaultConnection": "Host=127.0.0.1;Database=quantenginedb;Username=quantengine_app;Search Path=quantengine;"
   },
   "AllowedHosts": "*",
   "AdminSettings": {

src/dotnet/QuantEngine.Web/appsettings.json

@@ -7,7 +7,7 @@
   },
   "AllowedHosts": "*",
   "ConnectionStrings": {
-    "DefaultConnection": "Host=127.0.0.1;Database=quantenginedb;Username=quantengine_app;Password=quantengine_app;Search Path=quantengine;"
+    "DefaultConnection": "Host=127.0.0.1;Database=quantenginedb;Username=quantengine_app;Search Path=quantengine;"
   },
   "AdminSettings": {
     "Username": "admin",