Allow sorting the Issues feed by ingestion time, not just occurrence time

Customer request: allow sorting/filtering the Issues feed by when an event was ingested by Sentry, rather than only by occurrence-based Last Seen/First Seen. • Occurrence-based Last/First Seen correctly reflects when the underlying crash happened, but it's a poor signal for "what just arrived in Sentry" review queues. • This gap is most acute for teams triaging offline or high-latency clients, where delayed events can attach to existing issue groups without surfacing near the top of a Last Seen-sorted feed. • Without an ingestion-time sort, newly ingested delayed events are hard to find for review, especially when they merge into pre-existing groups instead of creating a new one. <!-- junior-request-attribution:start --> Requested by Michael Chai. <!-- junior-request-attribution:end --> <!-- junior-session-footer:start --> <!-- junior-conversation-id:slack%3AC0BUS8BRYLE%3A1788464757.381959 --> -- [View Junior Session]( [[Se…