Axiom Concurrency Profiling

When your Swift 6 build compiles clean but crashes in production with `_dispatch_assert_queue_fail` or `_swift_task_checkIsolatedSwift`, this is your diagnostic guide. It covers the runtime isolation bugs that static checking misses: Core Data `context.perform` crashes inside @MainActor classes, Combine `.map` closures inheriting wrong isolation, and delegate methods from CLLocationManager or WKNavigationDelegate that blow up despite zero warnings. Also includes the Swift Concurrency Instruments template for diagnosing actor contention and thread pool exhaustion. The source reveals this is part of a larger concurrency skill set, but the profiling angle specifically targets performance bottlenecks you can't see from compile time errors alone.