#11770 test: make the cmuxTests target compile again (main-actor call, CLI-only type)

Two PRs merged today left the cmuxTests target uncompilable, so every cmuxTests/... dispatch of test-e2e.yml ends with "Could not determine executed test count" and no unit test in the target runs (https://github.com/manaflow-ai/cmux/actions/runs/33707324236, https://github.com/manaflow-ai/cmux/actions/runs/33708419146).

1. https://github.com/manaflow-ai/cmux/pull/11524: productionPresenceIgnoresStagingEnvironment calls the main-actor static PresenceHeartbeatClient.resolvedServiceURL from a nonisolated synchronous test. Marked @MainActor, the pattern the other main-actor tests use.
2. https://github.com/manaflow-ai/cmux/pull/11529: ClaudeHookSessionStorePersistenceTests instantiates ClaudeHookSessionStore, which is defined in CLI/cmux.swift (the cmux-cli target) and is not visible to the app test bundle. It never compiled anywhere. Removed from the target; hook store behavior stays covered by the CLI-binary harness tests (ClaudeHookLiveDeliveryTargetTests and friends). A direct persistence test for the store needs to go through that harness.

Verification: test-e2e.yml on this branch with cmuxTests/VMClientTelemetryTests, which compiles the whole target and runs the tests added in https://github.com/manaflow-ai/cmux/pull/11755.