Make creating a person obvious; inline "create new" when linking relatives

- Family view gets a prominent "+ Add person" button that creates a person and
  opens their page to fill in details (previously you could only add a person
  via the empty-state form or by linking from another person).
- The person page's relationship picker (PersonCombobox) now offers
  "+ Create '<typed name>'" when the person doesn't exist yet: it creates them,
  links them in the chosen role (parent/child/partner/sibling), and jumps to
  their new page to edit — no more create-then-go-back-and-link.

Frontend only — no migration.

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

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

@@ -126,6 +126,12 @@ export default function FamilyViewPage() {
     return data?.id ?? null;
   }
 
+  // Create a new (blank) person and open their page to fill in details.
+  async function newPersonAndGo() {
+    const id = await addPerson("");
+    if (id) router.push(`/trees/${treeId}/persons/${id}`);
+  }
+
   async function createFirst(e: React.FormEvent) {
     e.preventDefault();
     if (!firstName.trim()) return;
@@ -352,12 +358,17 @@ export default function FamilyViewPage() {
     <div className="space-y-8">
       <div className="flex flex-wrap items-center justify-between gap-3">
         <h1 className="text-2xl font-semibold">Family view</h1>
-        <Link
-          href={`/trees/${treeId}/persons/${focus.id}`}
-          className="text-sm text-bronze hover:underline"
-        >
-          Open {focus.primary_name ?? "person"} →
-        </Link>
+        <div className="flex items-center gap-3">
+          <Button size="sm" onClick={newPersonAndGo}>
+            + Add person
+          </Button>
+          <Link
+            href={`/trees/${treeId}/persons/${focus.id}`}
+            className="text-sm text-bronze hover:underline"
+          >
+            Open {focus.primary_name ?? "person"} →
+          </Link>
+        </div>
       </div>
 
       {/* Pedigree: focus → parents → grandparents, with bracket connectors */}