refactor(backend): replace coravel with hangfire for background jobs

for *some reason*, coravel locks a persistent job queue behind a
paywall. this means that if the server ever crashes, all pending jobs
are lost. this is... not good, so we're switching to hangfire for that
instead.

coravel is still used for emails, though.

BREAKING CHANGE: Foxnouns.NET now requires Redis to work. the EFCore
storage for hangfire doesn't work well enough, unfortunately.

Foxnouns.Backend/Controllers/Authentication/EmailAuthController.cs

@@ -56,7 +56,7 @@ public class EmailAuthController(
         if (!req.Email.Contains('@'))
             throw new ApiError.BadRequest("Email is invalid", "email", req.Email);
 
-        string state = await keyCacheService.GenerateRegisterEmailStateAsync(req.Email, null, ct);
+        string state = await keyCacheService.GenerateRegisterEmailStateAsync(req.Email, null);
 
         // If there's already a user with that email address, pretend we sent an email but actually ignore it
         if (