fix(lifecycle): make logout nonblocking

[Andiveli]

Closes #376

Summary

• initiate remote logout without blocking the UI caller
• enforce single-flight result delivery and bounded cleanup
• coordinate reset generations to suppress stale results safely

Changes

File	Change
whatsrust/lib/client_lifecycle.go	Add asynchronous logout lifecycle and reset barriers
whatsrust/lib/client_lifecycle_test.go	Cover success, failure, timeout, reset, callbacks, and concurrency

Test plan

• Focused lifecycle tests passed
• Reset interleaving test passed 100 consecutive runs
• Full Go tests and race tests passed
• gofmt and diff checks passed

Review workload

Exactly 400 changed lines; no size exception required.

Checklist

• Linked approved issue
• Conventional commit
• No generated or unrelated changes