## Summary
- rename the `AlertManager` node role to `Scheduler` across Rust
services, jobs, protobuf bindings, UI labels, and tests
- emit `scheduler` as the canonical role name
- continue accepting legacy `alertmanager` and `alert_manager`
configuration values
- keep protobuf enum value `5` unchanged for wire compatibility
## Why
The role schedules and executes alerts, reports, pipelines, synthetics,
and other background work. `Scheduler` describes that broader
responsibility more accurately.
## Compatibility
- existing role configuration values remain accepted through parser and
serde aliases
- the protobuf numeric value remains stable
- coordinated changes are included in the Enterprise, Helm chart, and
documentation repositories
## Verification
- `cargo test -p config test_role`
- `cargo test -p openobserve-node`
- `cargo check -p openobserve-jobs`
- targeted web tests: 307 passed, 13 skipped
- Rust formatting and targeted Prettier checks