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/esign/[provider]/webhook/route.ts

@@ -0,0 +1,19 @@
+import { NextResponse } from "next/server"
+import { handleEsignWebhook, getAdapter } from "@/lib/esign"
+
+// Inbound e-signature status webhook (DocuSign Connect / Dropbox Sign callback).
+export async function POST(request: Request, { params }: { params: Promise<{ provider: string }> }) {
+  const { provider } = await params
+  if (!getAdapter(provider)) return NextResponse.json({ error: "unknown provider" }, { status: 404 })
+
+  const body = await request.text()
+  try {
+    await handleEsignWebhook(provider, body, request.headers)
+  } catch {
+    // never fail the webhook — providers retry on non-2xx
+  }
+
+  // Dropbox Sign requires this exact response body to validate the callback URL.
+  if (provider === "dropbox_sign") return new Response("Hello API Event Received", { status: 200 })
+  return NextResponse.json({ ok: true })
+}