Add project files.

GoogleApi/Models/ProviderModels.cs

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+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace GoogleApi.Models;
+
+/// <summary>
+/// Request from Gateway to GoogleApi.
+/// </summary>
+public sealed class ProviderRequest
+{
+    /// <summary>
+    /// Operation to execute (e.g., "Ping", "CreateCampaign", "GetCampaignStats")
+    /// </summary>
+    public string Operation { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Tenant/customer ID - maps to Google Ads customer ID (the subaccount)
+    /// </summary>
+    public string? TenantId { get; set; }
+
+    /// <summary>
+    /// Login customer ID - maps to Google Ads manager account (MCC)
+    /// Used in agency model where manager account accesses client subaccounts.
+    /// Populated by Gateway from tbAdAccount.accLoginAccountId.
+    /// </summary>
+    public string? LoginCustomerId { get; set; }
+
+    /// <summary>
+    /// Correlation ID for request tracing
+    /// </summary>
+    public string? RequestId { get; set; }
+
+    /// <summary>
+    /// Operation-specific payload
+    /// </summary>
+    public JsonElement? Payload { get; set; }
+
+    /// <summary>
+    /// Deserialize payload to strongly-typed object
+    /// </summary>
+    public T GetPayload<T>() where T : new()
+    {
+        if (Payload == null || Payload.Value.ValueKind == JsonValueKind.Null || Payload.Value.ValueKind == JsonValueKind.Undefined)
+            return new T();
+
+        try
+        {
+            return JsonSerializer.Deserialize<T>(Payload.Value.GetRawText(), JsonOptions.Default) ?? new T();
+        }
+        catch
+        {
+            return new T();
+        }
+    }
+}
+
+/// <summary>
+/// Response from GoogleApi to Gateway.
+/// </summary>
+public sealed class ProviderResponse
+{
+    public bool Ok { get; set; }
+    public string? RequestId { get; set; }
+    public object? Data { get; set; }
+    public ProviderError? Error { get; set; }
+
+    public static ProviderResponse Success(string? requestId, object? data = null)
+        => new() { Ok = true, RequestId = requestId, Data = data };
+
+    public static ProviderResponse Fail(string? requestId, string code, string message, object? detail = null)
+        => new()
+        {
+            Ok = false,
+            RequestId = requestId,
+            Error = new ProviderError { Code = code, Message = message, Detail = detail }
+        };
+}
+
+public sealed class ProviderError
+{
+    public string Code { get; set; } = "ERROR";
+    public string Message { get; set; } = "Unknown error";
+    public object? Detail { get; set; }
+}
+
+internal static class JsonOptions
+{
+    public static readonly JsonSerializerOptions Default = new(JsonSerializerDefaults.Web)
+    {
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
+    };
+}