fix: resolve TODO.md security/perf/test-coverage backlog

Fixes the 13-item codebase health scan backlog: wraps meal-plan
generation in a transaction, adds missing userId/GIN indexes, fixes
an IPv6-parsing gap in the webhook SSRF guard (and an identical
duplicated bug in the AI URL-import path, now consolidated onto one
implementation), paginates the collections list, dedupes the AI
recipe Zod schemas, wires up Stripe tier sync, rate-limits AI key
rotation, gets `pnpm typecheck` actually working, and adds test
coverage for the previously-untested admin/webhooks routes.

Two flagged issues (collection removeRecipeId IDOR, tier-limit race)
turned out to already be fixed/non-issues on inspection — noted in
TODO.md rather than silently dropped.

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

apps/web/app/api/v1/admin/test-email/route.ts

@@ -9,11 +9,16 @@ export async function POST(req: NextRequest) {
   const { to } = await req.json() as { to: string };
   if (!to) return NextResponse.json({ error: "Missing 'to'" }, { status: 400 });
 
+  const baseUrl = process.env["BETTER_AUTH_URL"];
+  if (!baseUrl) {
+    return NextResponse.json({ error: "BETTER_AUTH_URL is not configured" }, { status: 500 });
+  }
+
   try {
     await sendEmail({
       to,
       subject: "Epicure — test email",
-      html: verifyEmailHtml(`${process.env["BETTER_AUTH_URL"] ?? "http://localhost:3001"}/verify-email?token=test`),
+      html: verifyEmailHtml(`${baseUrl}/verify-email?token=test`),
     });
     return NextResponse.json({ ok: true });
   } catch (err) {