feat(family): platforms declared at inception and detected from bound repos (milestone 463 step 2, #4988)

A project's platforms decide which family ideas reach it. This step makes membership answerable from every door:

- services/platforms.py: the global catalog (writes are admin-only and duplicate-gated by slug); pure marker detection; and membership reads and writes. Detection only ADDS, and only where nobody has answered. It never overrides a declared or rejected row and never removes one.
- coverage: the archive scan now carries every path, and the refresh runs detection fail-open.
- inception: a platforms choice (slugs, or null for unanswered). The list is the whole answer: members left out of it become rejected.
- MCP: list_platforms and set_project_platforms; enter_project and get_project carry the project's platforms.
- REST: /api/platforms (admin writes) and /api/projects/<id>/platforms.
- UI: a platforms checklist on the inception card, a Family tab on ProjectView, and a Platforms admin tab in Settings.

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

frontend/src/stores/platforms.ts

@@ -0,0 +1,48 @@
+import { ref } from "vue";
+import { defineStore } from "pinia";
+import * as api from "@/api/platforms";
+import type { Platform } from "@/api/platforms";
+
+/**
+ * The global platform catalog (milestone 463). Shared by every project, so
+ * it is fetched once per session — as the canonical-area catalog is.
+ */
+export const usePlatformsStore = defineStore("platforms", () => {
+  const catalog = ref<Platform[]>([]);
+  const loaded = ref(false);
+  const loading = ref(false);
+
+  async function fetchCatalog(force = false) {
+    if (loaded.value && !force) return catalog.value;
+    loading.value = true;
+    try {
+      catalog.value = await api.listPlatforms();
+      loaded.value = true;
+    } catch {
+      // The catalog is a vocabulary for a form; an empty one degrades the
+      // form rather than failing the screen it sits on.
+      catalog.value = [];
+    } finally {
+      loading.value = false;
+    }
+    return catalog.value;
+  }
+
+  async function createEntry(data: { name: string; description?: string; markers?: string[] }) {
+    const entry = await api.createPlatform(data);
+    catalog.value.push(entry);
+    return entry;
+  }
+
+  async function updateEntry(
+    id: number,
+    data: Partial<{ name: string; description: string; order_index: number; markers: string[] }>,
+  ) {
+    const entry = await api.updatePlatform(id, data);
+    const idx = catalog.value.findIndex((p) => p.id === id);
+    if (idx >= 0) catalog.value[idx] = entry;
+    return entry;
+  }
+
+  return { catalog, loaded, loading, fetchCatalog, createEntry, updateEntry };
+});