Extract shared read_and_validate_config() with before/after mtime check
to detect mid-write config file changes. Add ReloadError enum with
FileChangedDuringRead variant. Return HTTP 409 Conflict on mtime change
from admin reload endpoint. Store cli_allow_wildcard_bind in
ConfigReloadHandle and use it in reload() validation instead of hardcoded
false. Update all ConfigReloadHandle::new() call sites.
glm-5.1
c6dda716f4