Consolidate audit-fixes branch: webhooks, integrations, and deploy hardening

Batch commit of the pending working tree on security/audit-fixes-2026-07.
Major areas:
- Outbound webhooks / Zapier: schema + signed delivery with retries, public
  v1 API (REST-hook subscribe/unsubscribe), settings UI, cron drain.
- Deploy hardening: email via SMTP2GO (Resend fully removed), verified DB TLS
  (DATABASE_SSL=require + DATABASE_CA), storage fails loud in production when
  Spaces is unconfigured instead of silently using ephemeral disk.
- Integrations & features (concurrent work): accounting (QuickBooks/Xero),
  e-signature (DocuSign/Dropbox Sign), PayPal, geocoding/maps, onboarding,
  expanded legal pages.
- DB migrations 0006–0009.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/api/cron/webhooks/route.ts

@@ -0,0 +1,16 @@
+import { NextResponse } from "next/server"
+import { isAuthorizedCron } from "@/lib/cron-auth"
+import { processDueDeliveries } from "@/lib/webhooks/deliver"
+
+// Webhook delivery retry drain. The emitter attempts an immediate delivery when
+// an event fires; this cron re-attempts anything still pending whose backoff
+// window has elapsed (and covers deliveries orphaned by a process restart).
+// Scheduled every 5 minutes via DigitalOcean Functions — see functions/project.yml.
+export async function GET(request: Request) {
+  if (!isAuthorizedCron(request)) {
+    return NextResponse.json({ error: "Unauthorized" }, { status: 401 })
+  }
+
+  const { processed, delivered } = await processDueDeliveries(200)
+  return NextResponse.json({ processed, delivered })
+}