fix: drop phantom ended-tab stubs, trust server as source of truth

[TeigenZhang]

Summary

The client cached open session tabs in localStorage and resurrected any that the server no longer knew about as grayed-out "ended" stubs. On multi-device use (close tab on mobile, open desktop) this left stale phantom tabs the user had to manually dismiss every time.

Fix

Drop the client-side resurrection path entirely; let the server be the source of truth for which sessions are open.

Removed:

• _restoreEndedTabs / _saveTabMetadata
• The session._ended branch in selectSession
• The data-ended render attribute and its matching CSS rule

Also clears the legacy localStorage key on init to purge stale entries left by previous client versions.

Net: -44 / +6 lines — removes complexity while fixing the UX bug.

Test plan

• tsc --noEmit passes
• npm run lint passes
• npm run format:check passes
• Manual verification: close a tab on mobile, refresh desktop — no phantom grayed-out tab appears.
• Manual verification: existing legacy localStorage entries from older clients are cleared on next page load.

[Ark0N]

Great input — thank you! Clean removal: the localStorage resurrection was the only thing that set _ended: true on the client, so dropping it along with all the consumers is consistent. Server-side ended status (via .tab-status.ended) is preserved for sessions the server still knows about. Merging.