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/components/ProjectFamilyTab.vue

@@ -0,0 +1,200 @@
+<script setup lang="ts">
+/**
+ * A project's place in the family (milestone 463): which platforms it is.
+ *
+ * Membership is what makes "does this family idea reach this project?" a
+ * lookup rather than a judgment — an idea is for some platforms, and it
+ * reaches every project that is one of them. So the answers here matter, and
+ * each kind of answer is shown as what it is:
+ *
+ * - Yes — a person said so.
+ * - Detected — a marker file in a bound repo said so. Detection only adds,
+ *   and only where nobody has answered; it never overrides a Yes or a No.
+ * - No — a person said this project is NOT that platform. Kept as a row, so
+ *   the next coverage refresh cannot detect it straight back.
+ * - No answer — detection may decide on the next refresh.
+ *
+ * Each change is saved as it is made: one platform, one request, applied
+ * whole or refused whole.
+ */
+import { computed, onMounted, ref, watch } from "vue";
+import { apiErrorMessage } from "@/api/client";
+import {
+  fetchProjectPlatforms, setProjectPlatforms,
+  type PlatformState, type ProjectPlatform, type SettablePlatformState,
+} from "@/api/platforms";
+import { usePlatformsStore } from "@/stores/platforms";
+
+const props = defineProps<{ projectId: number; canWrite: boolean }>();
+
+const platformsStore = usePlatformsStore();
+const answers = ref<ProjectPlatform[]>([]);
+const loading = ref(false);
+const failed = ref(false);
+const saving = ref<string | null>(null);
+const error = ref("");
+
+const LABELS: Record<PlatformState, string> = {
+  declared: "Yes",
+  detected: "Detected",
+  rejected: "No",
+};
+
+async function load() {
+  loading.value = true;
+  failed.value = false;
+  try {
+    const [, rows] = await Promise.all([
+      platformsStore.fetchCatalog(),
+      fetchProjectPlatforms(props.projectId),
+    ]);
+    answers.value = rows;
+  } catch {
+    // Said out loud: "couldn't load" must not read as "no platforms".
+    failed.value = true;
+  } finally {
+    loading.value = false;
+  }
+}
+
+const stateBySlug = computed(() => {
+  const out: Record<string, PlatformState> = {};
+  for (const a of answers.value) out[a.slug] = a.state;
+  return out;
+});
+
+const rows = computed(() =>
+  platformsStore.catalog.map((p) => ({
+    ...p,
+    state: stateBySlug.value[p.slug] ?? null,
+  })),
+);
+
+const memberCount = computed(
+  () => answers.value.filter((a) => a.state !== "rejected").length,
+);
+
+async function answer(slug: string, value: string) {
+  const state: SettablePlatformState = value === "" ? null : (value as SettablePlatformState);
+  saving.value = slug;
+  error.value = "";
+  try {
+    answers.value = await setProjectPlatforms(props.projectId, { [slug]: state });
+  } catch (e: unknown) {
+    error.value = apiErrorMessage(e, "Could not save that answer");
+  } finally {
+    saving.value = null;
+  }
+}
+
+onMounted(load);
+watch(() => props.projectId, load);
+</script>
+
+<template>
+  <div class="pft">
+    <header class="pft-head">
+      <h3 class="pft-title">Platforms</h3>
+      <p class="pft-muted">
+        What this project is built on or ships as. Ideas the family has proven
+        for a platform reach every project that is one, and each project
+        answers them — adopts, varies with a reason, or owes the work.
+      </p>
+    </header>
+
+    <p v-if="loading" class="pft-muted">Loading…</p>
+
+    <div v-else-if="failed" class="pft-note">
+      <strong>The platforms couldn't load.</strong>
+      <p>Nothing is known either way — this is a failure, not an empty answer.</p>
+      <button class="btn-secondary btn-sm" @click="load">Try again</button>
+    </div>
+
+    <p v-else-if="!rows.length" class="pft-muted">
+      This install has no platforms in its catalog yet. An administrator adds
+      them in Settings.
+    </p>
+
+    <template v-else>
+      <p class="pft-summary">
+        <template v-if="memberCount">
+          A member of {{ memberCount }} platform{{ memberCount === 1 ? "" : "s" }}.
+        </template>
+        <template v-else>
+          Not a member of any platform yet — bind a repo and refresh coverage
+          to detect them, or answer below.
+        </template>
+      </p>
+      <p v-if="error" class="error-msg">{{ error }}</p>
+      <ul class="pft-list">
+        <li v-for="p in rows" :key="p.id" class="pft-row">
+          <div class="pft-name">
+            <span>{{ p.name }}</span>
+            <span v-if="p.state" :class="['pft-tag', `pft-${p.state}`]">{{ LABELS[p.state] }}</span>
+            <span v-if="p.description" class="pft-desc">{{ p.description }}</span>
+          </div>
+          <select
+            v-if="canWrite"
+            class="pft-select"
+            :value="p.state === 'detected' ? 'detected' : (p.state ?? '')"
+            :disabled="saving === p.slug"
+            :aria-label="`Is this project ${p.name}?`"
+            @change="answer(p.slug, ($event.target as HTMLSelectElement).value)"
+          >
+            <option v-if="p.state === 'detected'" value="detected" disabled>Detected</option>
+            <option value="declared">Yes</option>
+            <option value="rejected">No</option>
+            <option value="">No answer</option>
+          </select>
+        </li>
+      </ul>
+    </template>
+  </div>
+</template>
+
+<style scoped>
+.pft { padding: 0.25rem 0; }
+.pft-head { margin-bottom: 1rem; }
+.pft-title { margin: 0 0 0.35rem; font-size: 1rem; }
+.pft-muted { color: var(--fs-text-tertiary); font-size: 0.875rem; margin: 0; }
+.pft-summary { color: var(--fs-text-secondary); font-size: 0.9rem; margin: 0 0 0.75rem; }
+.pft-note {
+  background: var(--fs-surface-raised);
+  border: 1px solid var(--fs-border-color);
+  border-radius: var(--fs-radius-md);
+  padding: 0.85rem 1rem;
+}
+.pft-note p { margin: 0.35rem 0 0.6rem; color: var(--fs-text-secondary); font-size: 0.875rem; }
+.pft-list { list-style: none; margin: 0; padding: 0; }
+.pft-row {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 1rem;
+  padding: 0.6rem 0;
+  border-bottom: 1px solid var(--fs-border-color);
+}
+.pft-name { display: flex; flex-wrap: wrap; align-items: baseline; gap: 0.25rem 0.5rem; min-width: 0; }
+.pft-desc { flex-basis: 100%; color: var(--fs-text-tertiary); font-size: 0.8rem; }
+.pft-tag {
+  font-size: 0.75rem;
+  padding: 0.05rem 0.45rem;
+  border-radius: var(--fs-radius-sm);
+  border: 1px solid var(--fs-border-color);
+  color: var(--fs-text-secondary);
+}
+.pft-declared { color: var(--fs-text-primary); }
+.pft-rejected { color: var(--fs-text-tertiary); text-decoration: line-through; }
+.pft-select {
+  padding: 0.35rem 0.6rem;
+  border: 1px solid var(--fs-border-color);
+  border-radius: var(--fs-radius-sm);
+  background: var(--fs-surface-page);
+  color: var(--fs-text-primary);
+  font-size: 0.85rem;
+  flex-shrink: 0;
+}
+@media (max-width: 640px) {
+  .pft-row { flex-direction: column; align-items: stretch; }
+}
+</style>