fix: replace print_and_exit() with Err(anyhow!(...))

[bsandu-peridio]

This fixes a deadlock in tui mode, because of tokio task error propagation. Can be reproduced by listing an extension under a runtime, but not defining in the extensions: section.

Flow chain before fix:

• spawned tokio task (ext build) hits stamp validation failure
• calls print_and_exit() → renderer.shutdown()
• shutdown() busy-waits with std::thread::sleep(5ms) for the render loop to stop
• std::thread::sleep() blocks the tokio thread, preventing the render loop task from running
• render loop never sets loop_stopped = true
• deadlock — shutdown() spins forever