Reload Extension Bundle

Trigger an atomic-swap reload for a single Bundle.

Returns the typed :class:~lfx.extension.reload.ReloadResult body on success. Per the typed-error contract, structural failures (broken bundle, missing source path, name mismatch) surface as 422 Unprocessable Entity with the first typed error in the body so clients can surface fix hints inline; the full ReloadResult payload (with all errors and warnings) is returned via the FastAPI detail envelope. Concurrency-control collisions surface as 409 Conflict (reload-in-progress). Non-2xx is the wire contract for every error path -- the body still carries the typed error so the client renders the same fix-hint envelope.