feat: developer access permission gates webhooks/API keys/BYOK (v0.71.0)

Webhooks, self-serve API keys, and BYOK AI provider keys had zero
access gating -- any logged-in user, any tier. Adds users.isDeveloper
(boolean, admin-toggled in admin/users/[id] alongside role/tier),
checked via a single hasDeveloperAccess() (lib/permissions.ts) so a
future subscription-tier auto-grant is a one-line change there, not
a redesign across call sites.

requireDeveloper() (lib/api-auth.ts) wraps requireSession() with a
fresh isDeveloper check (same reasoning as requireAdmin re-querying
role: session.user's cookieCache can be up to 5 minutes stale) and
replaces requireSession in all 8 gated routes: webhooks CRUD +
deliveries + redeliver, api-keys CRUD, ai-keys CRUD.

Settings UI: the sidebar hides API Keys/Webhooks nav entries for
non-developers; those pages and the BYOK section of Settings -> AI
show a locked notice instead of the manager component when accessed
directly.

Migration grandfathers in anyone who already has a webhook, API key,
or BYOK key row -- ships as a new gate on existing features, not a
silent lockout of active integrations.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/app/(app)/settings/layout.tsx

@@ -1,5 +1,6 @@
 import { headers } from "next/headers";
 import { auth } from "@/lib/auth/server";
+import { db, users, eq } from "@epicure/db";
 import { SettingsSidebar } from "@/components/settings/settings-sidebar";
 import { getMessages } from "@/lib/i18n/server";
 
@@ -7,6 +8,10 @@ export default async function SettingsLayout({ children }: { children: React.Rea
   const session = await auth.api.getSession({ headers: await headers() });
   const m = getMessages((session?.user as { locale?: string })?.locale);
 
+  const dbUser = session
+    ? (await db.select({ isDeveloper: users.isDeveloper }).from(users).where(eq(users.id, session.user.id)).limit(1))[0]
+    : undefined;
+
   return (
     <div className="max-w-5xl mx-auto">
       <div className="mb-8">
@@ -14,7 +19,7 @@ export default async function SettingsLayout({ children }: { children: React.Rea
         <p className="text-muted-foreground mt-1">{m.settings.subtitle}</p>
       </div>
       <div className="flex flex-col md:flex-row gap-4 md:gap-8 md:items-start">
-        <SettingsSidebar />
+        <SettingsSidebar isDeveloper={dbUser?.isDeveloper ?? false} />
         <main className="flex-1 min-w-0 space-y-6">{children}</main>
       </div>
     </div>