feat(DbExporter): create project structure and definition model

Add DbExporter tool project with:
- Project file targeting .NET 10 with required packages
  (protobuf-net-data, ZstdSharp.Port, Microsoft.Data.SqlClient,
  Oracle.ManagedDataAccess.Core)
- ExportDefinition model for JSON-based export configuration
- Placeholder Program.cs entry point

Tools/DbExporter/DbExporter.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="protobuf-net-data" Version="4.1.0" />
+    <PackageReference Include="ZstdSharp.Port" Version="0.8.1" />
+    <PackageReference Include="Microsoft.Data.SqlClient" Version="5.2.2" />
+    <PackageReference Include="Oracle.ManagedDataAccess.Core" Version="23.7.0" />
+  </ItemGroup>
+
+</Project>

Tools/DbExporter/ExportDefinition.cs

@@ -0,0 +1,21 @@
+using System.Text.Json.Serialization;
+
+namespace DbExporter;
+
+public sealed class ExportDefinition
+{
+    [JsonPropertyName("providerType")]
+    public required string ProviderType { get; init; }
+
+    [JsonPropertyName("connectionString")]
+    public required string ConnectionString { get; init; }
+
+    [JsonPropertyName("query")]
+    public required string Query { get; init; }
+
+    [JsonPropertyName("outputPath")]
+    public required string OutputPath { get; init; }
+
+    [JsonPropertyName("compressionLevel")]
+    public int CompressionLevel { get; init; } = 10;
+}

Tools/DbExporter/Program.cs

@@ -0,0 +1,9 @@
+namespace DbExporter;
+
+class Program
+{
+    static void Main(string[] args)
+    {
+        Console.WriteLine("DbExporter - Database Export Tool");
+    }
+}