feat: add email-api service and email-api-models contract project

New internal service that centralises SMTP email sending.
- email-api-models: SendEmailRequest DTO, IEmailApiClient Refit interface, EmailApiSettings
- email-api: SmtpEmailDispatcher (MailKit), EmailController (POST /api/email/send),
  branded HTML shell wrapper, shared-Files-volume attachment support
- Protected by X-Internal-Api-Key via UseInternalApiKeyProtection()
- No exposed Docker port — internal network only (http://email-api:8080)

Closes #22

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Apis/email-api/email-api.csproj

@@ -0,0 +1,27 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <DockerDefaultTargetOS>Linux</DockerDefaultTargetOS>
+    <RootNamespace>EmailApi</RootNamespace>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <NoWarn>$(NoWarn);1591</NoWarn>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="MailKit" />
+    <PackageReference Include="Serilog.AspNetCore" />
+    <PackageReference Include="Serilog.Enrichers.Environment" />
+    <PackageReference Include="Serilog.Sinks.Console" />
+    <PackageReference Include="Serilog.Sinks.Email" />
+    <PackageReference Include="Swashbuckle.AspNetCore" />
+    <PackageReference Include="Swashbuckle.AspNetCore.Annotations" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\Helpers\common-helpers\common-helpers.csproj" />
+    <ProjectReference Include="..\..\Helpers\startup-helpers\startup-helpers.csproj" />
+    <ProjectReference Include="..\api-models\api-models.csproj" />
+    <ProjectReference Include="..\common\common.csproj" />
+    <ProjectReference Include="..\email-api-models\email-api-models.csproj" />
+  </ItemGroup>
+</Project>