Add integration + Playwright smoke suite for post-deploy QA validation

Existing coverage was one integration test and zero e2e tests. Adds the thin,
high-value integration/e2e layer unit tests can't reach (real Postgres wire
contract, real browser flows) and wires it as a post-deploy smoke gate.

- Seed a deterministic dev/QA admin user and fixed Development env key so
  HTTP-only tests can authenticate without per-run registration.
- Expand the API integration suite: disabled-flag, unauthorized access,
  environment-document bootstrap, identity-override precedence, and auth
  login scenarios, reusing the existing black-box HTTP+Npgsql harness.
- Add a Playwright suite for the admin SPA: login, nav, project/environment
  context selection, and feature create/toggle, against the real API.
- Bind QA Postgres to 127.0.0.1 for direct seeding, add smoke-qa.sh and an
  ensure_node() bootstrap (the qa runner has no Node today), and wire a new
  smoke-qa CI job after deploy-qa.

tests/api/MicCheck.Api.Tests.Integration/MicCheck.Api.Tests.Integration.csproj

@@ -10,6 +10,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Identity.Core" Version="10.0.1" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.3.0" />
     <PackageReference Include="Npgsql" Version="10.0.1" />
     <PackageReference Include="NUnit" Version="4.5.1" />