fix: restructure inbox API routes — channel/ and message/ namespaces

Next.js не позволяет [channelId] и [id] на одном уровне.
Решение: /api/inbox/channel/[channelId]/* и /api/inbox/message/[id]/*
InboxTab: все fetch пути обновлены

app/api/inbox/message/[id]/reply/route.js

@@ -0,0 +1,17 @@
+import { NextResponse } from 'next/server';
+import { requireUser } from '@/lib/session';
+
+const ENGINE_URL    = process.env.ENGINE_URL    || 'http://localhost:3030';
+const ENGINE_SECRET = process.env.ENGINE_SECRET || '';
+
+export async function POST(req, { params }) {
+  const user = await requireUser();
+  if (!user) return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+  const body = await req.json().catch(() => ({}));
+  const res = await fetch(`${ENGINE_URL}/api/inbox/${params.id}/reply`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json', 'x-internal-secret': ENGINE_SECRET, 'x-user-id': String(user.id) },
+    body: JSON.stringify(body),
+  });
+  return NextResponse.json(await res.json());
+}

app/api/inbox/message/[id]/status/route.js

@@ -0,0 +1,17 @@
+import { NextResponse } from 'next/server';
+import { requireUser } from '@/lib/session';
+
+const ENGINE_URL    = process.env.ENGINE_URL    || 'http://localhost:3030';
+const ENGINE_SECRET = process.env.ENGINE_SECRET || '';
+
+export async function POST(req, { params }) {
+  const user = await requireUser();
+  if (!user) return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+  const body = await req.json().catch(() => ({}));
+  const res = await fetch(`${ENGINE_URL}/api/inbox/${params.id}/status`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json', 'x-internal-secret': ENGINE_SECRET, 'x-user-id': String(user.id) },
+    body: JSON.stringify(body),
+  });
+  return NextResponse.json(await res.json());
+}