Resolve file targets from labels (bur.volume / bur.path)

Extend discovery to read file-upload locations from the same labelled container.

• bur.volume (a named docker volume, repeatable) and bur.path (a host path) resolve into a per-app list of file targets.
• These labels live on the same container as the DB labels (for example issues-production-db-1), even though the data is mounted on a sibling app container. bur reads the path or volume from the label, not from that container's own mounts.

Acceptance

• one or more bur.volume labels and/or a bur.path resolve into a list of file targets.
• apps with neither are unaffected and stay DB-only.
• Issues resolves to path=/home/james/issues/prod/data/uploads.