Fix Credo Readability (strict)

- Max line length, implicit try, alias order, zero-arity defs
- String sigils, long comments split; redundant blank lines fixed

test/mv/oidc_role_sync_test.exs

@@ -92,7 +92,7 @@ defmodule Mv.OidcRoleSyncTest do
       # Minimal JWT: header.payload.signature with "groups" in payload (Rauthy puts groups in access_token)
       payload = Jason.encode!(%{"groups" => ["mila-admin"], "sub" => "oidc-123"})
       payload_b64 = Base.url_encode64(payload, padding: false)
-      header_b64 = Base.url_encode64("{\"alg\":\"HS256\",\"typ\":\"JWT\"}", padding: false)
+      header_b64 = Base.url_encode64(~s({"alg":"HS256","typ":"JWT"}), padding: false)
       sig_b64 = Base.url_encode64("sig", padding: false)
       access_token = "#{header_b64}.#{payload_b64}.#{sig_b64}"
       oauth_tokens = %{"access_token" => access_token}