Fix accidental 4.0 breaking changes and run example in CI

[OmegaJak]

This addresses two accidental breaking changes:

1. Introduced in telemetry: change LogVerbosity to an enum, use it throughout public API #14: Config deserialization previously expected log level to be all caps (e.g., "TRACE", matching slog), but are now expected to be lowercase (since foundations adds the serde attribute rename_all="snake_case" to enums). So deserialization of existing configs would break
2. Introduced in ZTC-1648: Avoid heap profiling crash by eagerly starting long-lived profiling thread #54: If an app has the "memory-profiling" feature enabled, but the settings disable memory profiling, server init would fail because the returned profiler would be None

This also adds adds a step to CI that does a "dry run" of the example to validate the example config, to help catch breaking config changes going forward