fix(stammbaum): guard inferred-relationship badge to single-receiver documents only

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/DocumentMetadataDrawer.svelte

@@ -113,7 +113,12 @@ function getFullName(person: Person): string {
 								{#each displayedReceivers as receiver, i (receiver.id)}
 									{@render personCard(
 										receiver,
-										i === 0 ? (inferredRelationship?.labelFromB ?? null) : null
+										// Badge only shown when there is exactly one receiver — with multiple
+										// receivers the inferred label is computed from the sender's viewpoint
+										// and cannot be attributed to a specific receiver.
+										i === 0 && receivers.length === 1
+											? (inferredRelationship?.labelFromB ?? null)
+											: null
 									)}
 								{/each}
 							</div>