test: add focused API controller coverage

[niemyjski]

Summary

• Add focused API controller coverage and tighten related controller-related tests.
• Update test coverage for authentication, organization, project, saved view, token, webhook, event, user, and admin controller flows.
• Keep behavior unchanged while improving confidence around API controller responses and edge cases.

Changes

• Add and adjust API controller tests in tests/Exceptionless.Tests/Controllers/*.
• Update supporting test infrastructure used by controller tests.
• Make small controller/test bootstrap adjustments needed for the new coverage.

Verification

• Limited local verification via targeted test updates and scoped test-focused changes in this commit.

Notes

• No API contract changes or breaking behavior changes.

[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
Exceptionless.AppHost	39%	40%	134	❌
Exceptionless.Core	72%	64%	8605	➖
Exceptionless.Insulation	24%	23%	203	❌
Exceptionless.Web	79%	67%	5189	✔
Summary	72% (17038 / 23536)	64% (8704 / 13596)	14131	➖