test: align suites with API and Console boundaries

[gbaudrit]

Summary

• introduce dedicated API, Console client, and Console component test projects
• keep standalone host composition and lifecycle coverage in Web.Tests
• remove executable host references from business-oriented test projects and retire Work.Api.Tests
• enforce the new boundaries through architecture tests
• align fast/integration solutions, CI thresholds, diagnostics, and documentation

Validation

• dotnet restore Agentstration.slnx
• dotnet build Agentstration.slnx --configuration Release --no-restore (0 warnings, 0 errors)
• fast lane: 336 passed
• integration lane: 512 passed, 3 optional scenarios skipped (515 total)

Closes #142