fix: preserve session recovery metadata during shutdown

[arzafran]

Terminal teardown can delete the metadata needed to reconnect a running session during an app update, even when the session holder retains that process. Preserve the metadata during shutdown and deallocation; remove it only after a finalized user close.

The teardown captures shutdown state before deferred cleanup and uses the same policy for process release and metadata deletion.

Validation:

• Regression commit: https://github.com/darkroomengineering/programa/actions/runs/35618669406 — retention fails; finalized-close deletion passes.
• Fix commit: https://github.com/darkroomengineering/programa/actions/runs/35620810431 — CI passes, including both platform builds, both unit shards, socket integration, and typing-latency checks.
• Unit logs record 1,840 passing cases and five existing skipped cases. Neither new regression test is skipped, and no assertions are relaxed.
• The optional UI-regression job was not enabled. A full in-app updater/relaunch was not exercised end-to-end.