fix: harden coroutine and stream ownership

[mkaltner]

Summary

• preserve coroutine cancellation across best-effort requests, polling, and live collectors
• give dashboard, Activity Center, terminal, logs, stats, project streams, and image transfers explicit target-aware ownership
• reject stale snapshot and stream results after refresh, environment removal, reconnect, or server replacement
• document the ownership model and mark PAR-008 complete with device evidence

Validation

• ./gradlew :app:testDebugUnitTest :app:assembleDebug
• 143 unit tests passed; debug APK assembled
• focused cancellation coverage passed across CoroutineFailuresTest, DashboardStreamStoreTest, CompleteListLoaderTest, and UpdaterRunScreenTest
• physical-device/live-server smoke test passed dashboard reconnect, environment switching, Activity Center refresh/departure, Logs/Stats/Terminal departure and reopen, and force-stop recovery