kona's NodeMode enum (crates/node/service/src/service/mode.rs) has only
Validator/Sequencer and parses via FromStr against the PascalCase display
strings. There is no 'verifier' mode, so the old value failed to parse and
kona-node crash-looped on startup. Validator is also kona's default.
Source change is env/op/kona.env (global default for all op-stack kona nodes),
so this regenerates KONA_NODE_MODE across all 38 op/*/...--kona compose files.