test: cover referral service tracking

[github-actions]

🤖 This is an automated pull request from Repo Assist, an automated AI assistant for this repository.

Summary

Adds integration coverage for ReferralService to protect referral tracking behavior:

• null users do not receive a referral ID
• valid referrers increment ReferralCount
• self-referrals are ignored
• unknown referral IDs do not alter users

Rationale

Referral tracking changes user state and relies on Identity claims plus EF Core bulk updates, but previously had no automated coverage. These tests use the existing SQLite-backed integration test factory and unique user IDs so they remain isolated when TUnit runs tests in parallel.

Test Status

• dotnet build EssentialCSharp.Web.Tests/EssentialCSharp.Web.Tests.csproj --no-restore --configuration Release — passed with 0 warnings and 0 errors.
• dotnet test EssentialCSharp.Web.Tests/EssentialCSharp.Web.Tests.csproj — 153 tests passed; two unrelated pre-existing integration tests failed (CaptchaService_Verify_Success and KnownBreachedPassword_IsDetected) because their external service responses were unavailable in this environment.

Warning

Firewall blocked 2 domains

The following domains were blocked by the firewall during workflow execution:

• api.hcaptcha.com
• api.pwnedpasswords.com

To allow these domains, add them to the network.allowed list in your workflow frontmatter:

network:
  allowed:
    - defaults
    - "api.hcaptcha.com"
    - "api.pwnedpasswords.com"

See Network Configuration for more information.

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[Copilot]

🟢 Approval recommended

The focused test-only changes match the service behavior, with no blocking issues identified.

No open issues 🎉

What changed in this PR

Adds integration coverage for referral tracking using the existing SQLite-backed test infrastructure.

Changes:

• Covers null users, valid referrals, self-referrals, and unknown referral IDs.
• Verifies referral counts and protects unrelated users from changes.
• Uses unique user IDs to isolate test data.

File	Description
EssentialCSharp.Web.Tests/​ReferralServiceTests.cs	Adds four referral service tests and user setup/query helpers.

_{Review effort: Balanced}

[Copilot]

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