Move amber/web onto the in-house JwtAuthFilter

### Task Summary

Once Dropwizard 4 is in place in amber and the namespace migration is complete, replace amber's toastshaman wiring with the in-house `org.apache.texera.auth.JwtAuthFilter` that the five microservices already use. Concretely:

- `amber/src/main/scala/org/apache/texera/web/TexeraWebApplication.scala` and `ComputingUnitMaster.scala`: replace `setupJwtAuth(environment)` calls with the in-house registration pattern (`AuthDynamicFeature(classOf[JwtAuthFilter])` + `UnauthorizedExceptionMapper` + `AuthValueFactoryProvider.Binder` + `RolesAllowedDynamicFeature`)
- Delete `amber/src/main/scala/org/apache/texera/web/auth/JwtAuth.scala`, `UserAuthenticator.scala`, `UserRoleAuthorizer.scala`
- Remove the `com.github.toastshaman:dropwizard-auth-jwt` dependency from `amber/build.sbt`

The behavior delta is small but visible: amber's challenge changes from `Bearer realm="realm"` to `Bearer realm="texera"`, and invalid-token responses gain the `error="invalid_token"` parameter the in-house filter already emits for the other services. Closes the unification tracked under #4901.

Part of #5423. Closes #4901 once landed.

### Task Type

- [x] Refactor / Cleanup