feat: establish dotnet engineering foundation

Tiku.Api/Options/OptionsValidation.cs

@@ -1,7 +1,42 @@
+using Microsoft.Extensions.Configuration;
+using Tiku.Application.Security;
+
 namespace Tiku.Api.Options;
 
 public static class OptionsValidation
 {
+    public const string DevelopmentSigningKey = "development-only-tiku-signing-key-change-before-production";
+
+    public static string ResolveDatabaseConnectionString(
+        IConfiguration configuration,
+        bool isDevelopment)
+    {
+        var connectionString =
+            configuration.GetConnectionString("Database") ??
+            configuration["DATABASE_URL"];
+        if (!string.IsNullOrWhiteSpace(connectionString))
+        {
+            return connectionString;
+        }
+
+        if (isDevelopment)
+        {
+            return $"Host=localhost;Database=tiku;Username={Environment.UserName}";
+        }
+
+        throw new InvalidOperationException(
+            "Database connection is required outside Development. Configure ConnectionStrings:Database or DATABASE_URL.");
+    }
+
+    public static bool BeValidJwtOptions(JwtOptions options, bool isProduction)
+    {
+        return !isProduction ||
+               !string.Equals(
+                   options.SigningKey,
+                   DevelopmentSigningKey,
+                   StringComparison.Ordinal);
+    }
+
     public static bool BeValidCorsOptions(CorsOptions options)
     {
         if (options.AllowCredentials && options.AllowedOrigins.Length == 0)