feat(family): an idea links to the rule topic holding its norms - set_family_topic, the readouts name the rules, the idea row shows the link (milestone 463 step 1 gap, found in step 7, #4993)

Step 1 added family_ideas.topic_id but nothing could set it, so the note<->topic
link the milestone promised existed only as a column. set_family_topic links or
unlinks (0) a topic in a rulebook the caller owns, one idea per topic; the
version does not move. get_family_idea and get_family_adoption list the topic's
rules; list_family_ideas and the Family page name the topic. The model
docstrings no longer claim the topic's rules are platform-scoped in retrieval.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/views/FamilyView.vue

@@ -259,6 +259,12 @@ onMounted(load);
               <div v-if="idea.platforms.length" class="fam-platforms">
                 <code v-for="p in idea.platforms" :key="p" class="fam-chip">{{ p }}</code>
               </div>
+              <p v-if="idea.topic" class="fam-muted fam-topic">
+                Binding rules:
+                <router-link
+                  :to="{ path: '/rules', query: { rb: String(idea.topic.rulebook_id), topic: String(idea.topic.id) } }"
+                >{{ idea.topic.title }}</router-link>
+              </p>
             </div>
             <button
               v-if="idea.status !== 'retired'"
@@ -376,6 +382,7 @@ onMounted(load);
 .fam-row-title { display: flex; flex-wrap: wrap; align-items: baseline; gap: 0.25rem 0.5rem; }
 .fam-applies { margin: 0.3rem 0 0; font-size: 0.85rem; color: var(--fs-text-secondary); }
 .fam-platforms { display: flex; flex-wrap: wrap; gap: 0.3rem; margin-top: 0.35rem; }
+.fam-topic { margin: 0.35rem 0 0; }
 .fam-chip {
   font-family: var(--fs-font-mono);
   font-size: 0.72rem;