Change /api/search logic to Neynar search

[hellno]

instead of querying our own DB, we can switch to Neynar's API endpoint: https://docs.neynar.com/reference/cast-search

this includes removing code related to DB scheme and SQL queries.
functionality should be kept as much as possible, but some filters are not available on Neynar search (yet), so we can remove them for now

[hellno]

currently we only have 'Power Badge' filter, we can adjust this to say 'Priority Mode' and use the priority_mode filter on the Neynar endpoint