Fix CI failures and add opt-in live E2E concurrency validation

[Doug Guthrie (dpguthrie)]

Summary

• restore missing concurrency/pipeline config and client plumbing expected by current tests
• wire max_concurrent_resources through orchestrator migration phases
• make base migrator pass max_concurrent only to migrators that support it
• accept max_concurrent in LogsMigrator.migrate_all for interface compatibility
• add opt-in live smoke test and opt-in live E2E matrix test for real-org validation

Validation

• local unit/integration suite passes
• live smoke test passed against real source/destination orgs
• live E2E matrix run passed after logs signature fix