chore(web.api): add UserSecretsId for local dev secrets (OAuth keys via user-secrets)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Web.Api/Web.Api.csproj

@@ -1,9 +1,10 @@
-<Project Sdk="Microsoft.NET.Sdk.Web">
+<Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
     <TargetFramework>net10.0</TargetFramework>
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
+    <UserSecretsId>3c382f4e-81a2-4b63-929f-fefd29e950e8</UserSecretsId>
   </PropertyGroup>
 
   <ItemGroup>