fix: migrate to go-jwt-middleware v3 API

- Use validator and jwks packages for JWT validation
- Replace manual JWKS caching with jwks.NewCachingProvider
- Add CustomClaims struct for https://unbound.se/roles claim
- Rename TokenFromContext to ClaimsFromContext
- Update middleware/auth.go to use new claims structure
- Update tests to use core.SetClaims and validator.ValidatedClaims

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

go.mod

@@ -9,10 +9,8 @@ require (
 	github.com/alecthomas/kong v1.13.0
 	github.com/apex/log v1.9.0
 	github.com/auth0/go-jwt-middleware/v3 v3.0.0
-	github.com/golang-jwt/jwt/v5 v5.3.0
 	github.com/google/uuid v1.6.0
 	github.com/jmoiron/sqlx v1.4.0
-	github.com/pkg/errors v0.9.1
 	github.com/pressly/goose/v3 v3.26.0
 	github.com/rs/cors v1.11.1
 	github.com/sparetimecoders/goamqp v0.3.3
@@ -60,6 +58,7 @@ require (
 	github.com/lestrrat-go/option/v2 v2.0.0 // indirect
 	github.com/lib/pq v1.10.9 // indirect
 	github.com/mfridman/interpolate v0.0.2 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/rabbitmq/amqp091-go v1.10.0 // indirect
 	github.com/segmentio/asm v1.2.1 // indirect