fix(desktop): keep restarted sessions on their owner

[mr-magaia]

What

• Keep selected and tiled stored-session owner scopes foregrounded after restart.
• Retain a cold-resume owner until the runtime publishes foreground state.
• Keep explicit local profile selections on This device.
• Accept backend READY announcements from stderr or buffered output.

Why

After restart, a stored session in All Profiles can have no live runtime scope yet. The idle pruner then closes its owner socket, causing repeated loader flashes. The previous hold only delayed that failure. The current hermes serve process can also emit READY on stderr, and local profile picks could fall through the legacy remote primary route.

Verification

• 69 targeted desktop tests passed.
• Desktop type-check passed.
• Signed macOS build passed codesign --verify --deep --strict.
• Exact-head UI checks: default, Daniela, Dexter, James, and Mali stayed on This device with zero post-ready anomalies.
• Exact-head All Profiles persisted-session watch: 25 of 25 clean samples.
• Longer All Profiles watch before the final upstream rebase: 85 of 85 clean samples.

No new dependencies.