Computed reverse relationships — purely frontend, no Rust changes.
The useReferencedBy hook scans all entries' relationships maps to find
those referencing the current note via frontmatter wikilinks.
References are grouped by relationship key (e.g. "via Belongs to",
"via Related to") and displayed between Relationships and Backlinks.
Architecture decision: "Referenced by" is read-only. To remove a
reverse reference, navigate to the source note. Deleting a note
automatically removes it from all computed reverse references.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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