Fixes a bug where the UI would freeze when processing citation sources with mixed distance metrics.
The `Citations.svelte` component was attempting to call `.push()` on an `undefined` `distances` array. This happened when the first document for a source had no distance value, but a subsequent document for the same source did.
This patch ensures the `distances` array is always initialized as an empty array `[]` instead of `undefined`, preventing the `TypeError` and resolving the UI freeze.
7222a9aef6