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/api/family.ts

@@ -17,12 +17,23 @@ export interface Criterion {
   test: string;
 }
 
+export interface IdeaTopic {
+  id: number;
+  title: string;
+  rulebook_id: number;
+  /** Present on a single idea's read, not on the list. */
+  rules?: { id: number; title: string }[];
+}
+
 export interface FamilyIdea {
   note_id: number;
   status: IdeaStatus;
   applies_when: string;
   canon_version: number;
   topic_id: number | null;
+  /** The rule topic holding the idea's binding norms; null when none is
+   *  linked or the reader does not own its rulebook. */
+  topic: IdeaTopic | null;
   title: string;
   note_type: string;
   is_task: boolean;