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/api/v1/ai-keys/route.ts

@@ -1,7 +1,7 @@
 import { NextResponse } from "next/server";
 import { z } from "zod";
 import { db, userAiKeys, eq, and } from "@epicure/db";
-import { requireSession } from "@/lib/api-auth";
+import { requireDeveloper } from "@/lib/api-auth";
 import { encrypt } from "@/lib/encrypt";
 import { applyRateLimit } from "@/lib/rate-limit";
 
@@ -13,7 +13,7 @@ const PostSchema = z.object({
 });
 
 export async function GET() {
-  const { session, response } = await requireSession();
+  const { session, response } = await requireDeveloper();
   if (response) return response;
 
   const keys = await db.query.userAiKeys.findMany({
@@ -25,7 +25,7 @@ export async function GET() {
 }
 
 export async function POST(req: Request) {
-  const { session, response } = await requireSession();
+  const { session, response } = await requireDeveloper();
   if (response) return response;
 
   const limited = await applyRateLimit(`rl:ai-keys:${session!.user.id}`, 5, 3600);