Replace main site with rebranding notice

[taesungh]

For 2024, this hackathon was rebranded to IrvineHacks. There was a case of one interested participant who was unaware of the name change and was bamboozled waiting for an update on the HackUCI website and missed the deadline to apply in January.

Accordingly, we should replace the main site with a notice that HackUCI is now IrvineHacks with a link to the new website. The old site design(s) can remain internally for reference/historical purposes (deployment details TBD).