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/api/platforms.ts

@@ -0,0 +1,77 @@
+/**
+ * Platforms — what a project is built on or ships as (milestone 463).
+ *
+ * The catalog is GLOBAL, like the canonical areas, and admin-written. A
+ * project's answer per platform is `declared` (a person said so), `detected`
+ * (a marker file in a bound repo said so) or `rejected` (a person said no —
+ * kept, so the next refresh cannot detect it back). Only declared and
+ * detected make a project a member, and membership is what decides which
+ * family ideas reach it.
+ */
+import { apiGet, apiPatch, apiPost, apiPut } from "@/api/client";
+
+export interface Platform {
+  id: number;
+  name: string;
+  /** The match key, and the name every door takes (stable across restores). */
+  slug: string;
+  description: string | null;
+  /** Repo-relative globs. A bare name matches a basename anywhere; one with
+   *  a slash matches the whole path. Empty = declare-only. */
+  markers: string[];
+  order_index: number;
+  created_at: string | null;
+  updated_at: string | null;
+}
+
+export type PlatformState = "declared" | "detected" | "rejected";
+/** What a person may set. `null` withdraws the answer. */
+export type SettablePlatformState = "declared" | "rejected" | null;
+
+export interface ProjectPlatform {
+  id: number;
+  slug: string;
+  name: string;
+  state: PlatformState;
+}
+
+export const MEMBER_STATES: PlatformState[] = ["declared", "detected"];
+
+export async function listPlatforms(): Promise<Platform[]> {
+  const data = await apiGet<{ platforms: Platform[] }>("/api/platforms");
+  return data.platforms;
+}
+
+/** Admin only. A name that reduces to an existing slug answers 409. */
+export async function createPlatform(data: {
+  name: string;
+  description?: string;
+  markers?: string[];
+}): Promise<Platform> {
+  return apiPost("/api/platforms", data);
+}
+
+export async function updatePlatform(
+  id: number,
+  data: Partial<{ name: string; description: string; order_index: number; markers: string[] }>,
+): Promise<Platform> {
+  return apiPatch(`/api/platforms/${id}`, data);
+}
+
+export async function fetchProjectPlatforms(projectId: number): Promise<ProjectPlatform[]> {
+  const data = await apiGet<{ project_platforms: ProjectPlatform[] }>(
+    `/api/projects/${projectId}/platforms`,
+  );
+  return data.project_platforms;
+}
+
+/** Only the slugs named change; the update applies whole or not at all. */
+export async function setProjectPlatforms(
+  projectId: number,
+  platforms: Record<string, SettablePlatformState>,
+): Promise<ProjectPlatform[]> {
+  const data = await apiPut<{ project_platforms: ProjectPlatform[] }>(
+    `/api/projects/${projectId}/platforms`, { platforms },
+  );
+  return data.project_platforms;
+}