MFS — register / update / re-sync data sources

1. What this skill does

Walks the user through getting a data source into MFS so it's searchable. The work splits into:

1. Picking the right connector scheme.
2. Collecting credentials (preferring env:VAR / file:/path indirection over plaintext).
3. Writing a connector TOML.
4. Calling mfs add <uri> --config <toml> and monitoring the returned job.

Each connector has its own field set, credential acquisition story, and gotchas. Per-connector details live in reference/connectors/<scheme>.md — read the matching one before collecting fields for any scheme.

Step 0: Pre-flight (always run first)