Local filesystem paths leak into published schema validation errors

[lukejudd-lux]

Issue

flowctl publish can bake local file:// schema paths into published specs. These paths later appear in runtime validation errors, exposing user workstation paths.

Expected Behavior

Published specs should not retain local machine paths.

Suggested Fix

Sanitise local schema $ids during bundle/author/publish, for example:

file:///Users/alice/project/schemas/foo.yaml

to something like:

flow://source/schemas/foo.yaml