feat(family): the adoption ledger - assessment, the conflict order, owed->task, recheck, the adoption matrix (milestone 463 step 4, #4990)

- services/family_adoption.py: assess one project against one canon idea by
  the four outcomes in order (exempt, variant, adopted, owed). Every outcome
  needs a reason and adopted needs evidence. The engine records the precedents
  itself: this idea's answers elsewhere, and this project's answers to the
  nearest ideas. The same answer given twice records nothing.
- owed files a task in the OWING project, tagged to the System matching the
  idea's canonical area, naming the gap and the reference for that project's
  language. The task follows the answer: adopted closes it, exempt or variant
  cancels it, owed again reopens it. Each move is logged on the task.
- the conflict order is enforced: every ground above the deciding one must
  say why it did not decide. The losing side is folded into the idea's note as
  a trap, an alternative or a condition branch, the version moves, and both
  rows are answered against the revision.
- recheck is derived (row version != idea version). family.revise moves the
  version when substance changes. undo covers a project's latest answer too.
- set_family_references names the reference implementations.
- MCP: get/list/assess adoption, resolve_family_conflict, revise_family_idea,
  set_family_references. Web: GET /api/family/matrix.
- UI: an adoption matrix on /family (platform filter, cell detail with reason,
  recheck and owed-task link) and the same matrix narrowed to one project on
  its Family tab. The decision log now reads project-level decisions.

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

frontend/src/components/ProjectFamilyTab.vue

@@ -16,6 +16,10 @@
  *
  * Each change is saved as it is made: one platform, one request, applied
  * whole or refused whole.
+ *
+ * Below the platforms: this project's answer to each canon idea that reaches
+ * it — the adoption matrix narrowed to one row, so it reads exactly as the
+ * family page does.
  */
 import { computed, onMounted, ref, watch } from "vue";
 import { apiErrorMessage } from "@/api/client";
@@ -24,6 +28,7 @@ import {
   type PlatformState, type ProjectPlatform, type SettablePlatformState,
 } from "@/api/platforms";
 import { usePlatformsStore } from "@/stores/platforms";
+import FamilyAdoptionMatrix from "@/components/FamilyAdoptionMatrix.vue";
 
 const props = defineProps<{ projectId: number; canWrite: boolean }>();
 
@@ -150,6 +155,11 @@ watch(() => props.projectId, load);
         </li>
       </ul>
     </template>
+
+    <section class="pft-answers" aria-labelledby="pft-answers-title">
+      <h3 id="pft-answers-title" class="pft-title">Family ideas</h3>
+      <FamilyAdoptionMatrix :key="projectId" :project-id="projectId" />
+    </section>
   </div>
 </template>
 
@@ -195,6 +205,7 @@ watch(() => props.projectId, load);
   font-size: 0.85rem;
   flex-shrink: 0;
 }
+.pft-answers { margin-top: 1.75rem; }
 @media (max-width: 640px) {
   .pft-row { flex-direction: column; align-items: stretch; }
 }