Add family tree page, linked from the NPC's family name

- /npcs/family/{family} (app_npc_family) renders a parent->child tree for
  everyone sharing that family name; co-parents who are both in the family
  are paired into one couple node, elders first
- FamilyTreeBuilder does the flat-list -> tree assembly
- the NPC detail page's family name (subtitle + Details row) now links there
- .family-tree CSS: nested list with connector lines, small portrait avatars

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

assets/styles/app.css

@@ -23,3 +23,69 @@ main.app-main {
 table.dataTable {
     width: 100% !important;
 }
+
+/* --- Family tree --------------------------------------------------------- */
+.family-tree,
+.family-tree ul {
+    list-style: none;
+    margin: 0;
+    padding-left: 1.25rem;
+}
+.family-tree {
+    padding-left: 0;
+}
+.family-tree li {
+    position: relative;
+    padding: 0.15rem 0 0.15rem 1rem;
+}
+.family-tree ul > li::before {      /* elbow connector */
+    content: "";
+    position: absolute;
+    top: 0;
+    left: 0;
+    bottom: 50%;
+    width: 0.75rem;
+    border-left: 1px solid var(--bs-border-color);
+    border-bottom: 1px solid var(--bs-border-color);
+}
+.family-tree ul > li::after {       /* line continuing to siblings below */
+    content: "";
+    position: absolute;
+    top: 0;
+    left: 0;
+    height: 100%;
+    border-left: 1px solid var(--bs-border-color);
+}
+.family-tree ul > li:last-child::after {
+    display: none;
+}
+.ft-couple {
+    display: inline-flex;
+    align-items: center;
+    gap: 0.4rem;
+    flex-wrap: wrap;
+}
+.ft-person {
+    display: inline-flex;
+    align-items: center;
+    gap: 0.45rem;
+    padding: 0.2rem 0.5rem;
+    border: 1px solid var(--bs-border-color);
+    border-radius: 0.375rem;
+    text-decoration: none;
+    color: inherit;
+    background: var(--bs-body-bg);
+}
+.ft-person:hover {
+    border-color: var(--bs-primary);
+}
+.ft-name {
+    font-weight: 500;
+}
+.ft-meta {
+    font-size: 0.8125rem;
+    color: var(--bs-secondary-color);
+}
+.ft-amp {
+    color: var(--bs-secondary-color);
+}