test(interview): migrate suites to held-port helper + bounded fetches

Replace the four private findFreePort bind/close/bind helpers with
bindFreePort() from src/interview/test-port.ts. Dashboard-role managers
now adopt the held server via the new `server` option (session-role
managers reuse the port number); afterEach closes any held server that
was never adopted. Bare localhost fetches in manager.test.ts get
AbortSignal.timeout(2000) so a stuck connection fails fast instead of
hanging the suite.