Retain active session from Home - #10

What changed

• add a Home action to the connected transcript and terminal screen
• keep the single foreground-service-backed SSH session active while Home is open
• show the active session with explicit Return and Disconnect actions
• disable starting a second connection until the active session ends
• preserve connected-screen draft and mode state across the Home round trip, then clear it when the session ends
• update current alpha documentation and backlog boundaries

Why

Physical alpha testing showed that reaching profiles, trust records, or transcript history required disconnecting. This adds the smallest useful navigation model without introducing concurrent sessions or a larger session manager.

Impact

Leaving the connected screen no longer implies disconnecting. Multiple concurrent sessions remain out of scope.

Checks

• ./gradlew test lint assembleDebug assembleRelease connectedDebugAndroidTest
• ./scripts/test-sign-latest-alpha.sh
• ./scripts/verify-release-shrinker-contracts.sh
• focused Home, active-session card, disconnect separation, and 200 percent font-scale Compose tests
• git diff --check and staged leak review