Shared marriage events; deterministic parent ordering

- Partnership life events (marriage/divorce/engagement) now attach to the
  couple's relationship, not each person. The add-event form asks for the
  spouse, finds-or-creates the partnership, and writes ONE event on it — shown
  on both partners' pages ("· with <spouse>"), entered once. Event values
  (RELI/OCCU detail) now render too.
- Family-view pedigree orders parents deterministically (father on top, mother
  below, stable fallback when gender is unknown) instead of by which link was
  created first.

Frontend only — no migration.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/app/trees/[id]/page.tsx

@@ -86,8 +86,18 @@ export default function FamilyViewPage() {
   }, [search, treeId]);
 
   const byId = useMemo(() => new Map(people.map((p) => [p.id, p])), [people]);
+  // Order parents deterministically: father (male) on top, mother below, with a
+  // stable fallback when gender is unknown (so it doesn't depend on which link
+  // happened to be created first).
+  const parentRank = (id: string) => {
+    const g = byId.get(id)?.gender;
+    return g === "male" ? 0 : g === "female" ? 1 : 2;
+  };
   const parentsOf = (id: string) =>
-    rels.filter((r) => r.type === "parent_child" && r.person_to_id === id).map((r) => r.person_from_id);
+    rels
+      .filter((r) => r.type === "parent_child" && r.person_to_id === id)
+      .map((r) => r.person_from_id)
+      .sort((a, b) => parentRank(a) - parentRank(b));
   const childrenOf = (id: string) =>
     rels.filter((r) => r.type === "parent_child" && r.person_from_id === id).map((r) => r.person_to_id);
   const partnersOf = (id: string) =>