fix(security): tier-0 audit blockers (next CVE, role gate, perm traps, key validation, rate limits)

Closes the five highest-risk findings from
docs/audit-comprehensive-2026-05-05.md so the platform is not exposed
while the rest of the audit backlog (1 CRIT + 18 HIGH + 32 MED + 23 LOW)
is worked through:

* CVE-2025-29927 — bump next 15.1.0 → 15.2.9; nginx strips
  X-Middleware-Subrequest at the edge as defense-in-depth.
* Cross-tenant role escalation — POST/PATCH/DELETE on /admin/roles now
  require super-admin (was: any holder of admin.manage_users).  Adds
  shared `requireSuperAdmin(ctx)` helper.
* Silent-403 traps — `documents.edit` and `files.edit` keys added to
  RolePermissions; seeded role values updated; migration 0041 backfills
  the new keys on every existing roles+port_role_overrides JSONB.  File
  routes remap the dead `create` action to `upload` / `manage_folders`.
* Berth-PDF / brochure register endpoints — reject body.storageKey
  unless it matches the namespace the matching presign endpoint issued
  (prevents repointing a tenant's PDF at foreign-port bytes).
* Portal auth rate limits — sign-in 5/15min/(ip,email),
  forgot-password 3/hr/IP, activate/reset/set-password 10/hr/IP.  Adds
  `enforcePublicRateLimit()` for non-`withAuth` routes.

Test status unchanged: 1168/1168 vitest, tsc clean.

Refs: docs/audit-comprehensive-2026-05-05.md (CRITICAL, HIGH §§1–4)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/api/portal/auth/sign-in/route.ts

@@ -4,6 +4,7 @@ import { z } from 'zod';
 import { errorResponse } from '@/lib/errors';
 import { PORTAL_COOKIE } from '@/lib/portal/auth';
 import { signIn } from '@/lib/services/portal-auth.service';
+import { enforcePublicRateLimit } from '@/lib/api/route-helpers';
 
 const bodySchema = z.object({
   email: z.string().email(),
@@ -17,14 +18,24 @@ export async function POST(req: NextRequest): Promise<NextResponse> {
   try {
     body = await req.json();
   } catch {
-    return NextResponse.json({ error: 'Invalid request body' }, { status: 400 });
+    return NextResponse.json({ error: 'Email format is invalid' }, { status: 400 });
   }
 
   const parsed = bodySchema.safeParse(body);
   if (!parsed.success) {
-    return NextResponse.json({ error: 'Invalid email or password' }, { status: 400 });
+    return NextResponse.json({ error: 'Email format is invalid' }, { status: 400 });
   }
 
+  // Per-(ip,email) bucket: 5 attempts / 15min. Keyed on email-lowercase so
+  // the limiter is per-account-per-IP, not just per-IP — a NATed network
+  // shouldn't be able to lock a single victim by burning their bucket.
+  const limited = await enforcePublicRateLimit(
+    req,
+    'portalSignIn',
+    parsed.data.email.toLowerCase(),
+  );
+  if (limited) return limited;
+
   try {
     const result = await signIn(parsed.data);
     const res = NextResponse.json({ success: true });