Wiki write-path operations (most commonly `wiki +node-create` against the
same parent) surface code 131009 "lock contention" under concurrent calls.
Currently this falls through to the generic "api_error" classification,
giving users no hint that it is transient and safe to retry.
Mirror the existing `LarkErrDriveResourceContention` (1061045) treatment:
add a named constant, classify as "conflict", and emit a hint that points
the caller toward exponential backoff or serializing sibling-node writes.
Refs: #1012
f2a4c95665