Adds a `relationships: HashMap<String, Vec<String>>` field to VaultEntry that captures ALL frontmatter fields containing wikilinks (e.g. Has, Topics, Events, Notes, Buckets, Highlights). Handles both single string and array values. Known non-relationship keys (Is A, aliases, Status, etc.) are skipped. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>