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>

lib/turnstile.ts

@@ -0,0 +1,37 @@
+const VERIFY_URL = "https://challenges.cloudflare.com/turnstile/v0/siteverify"
+
+/**
+ * Verifies a Cloudflare Turnstile token server-side against the siteverify API.
+ *
+ * Fails CLOSED when Turnstile is configured (secret present) but the token is
+ * missing or invalid. Fails OPEN only when `TURNSTILE_SECRET_KEY` is unset — so
+ * environments that haven't configured Turnstile keep working, matching how the
+ * other optional integrations (Stripe / OpenAI / SMTP email) degrade in this app.
+ */
+export async function verifyTurnstile(
+  token: string | undefined | null,
+  remoteIp?: string | null
+): Promise<boolean> {
+  const secret = process.env.TURNSTILE_SECRET_KEY
+  if (!secret) return true // integration disabled — do not block auth
+  if (!token) return false
+
+  try {
+    const body = new URLSearchParams()
+    body.append("secret", secret)
+    body.append("response", token)
+    if (remoteIp) body.append("remoteip", remoteIp)
+
+    const res = await fetch(VERIFY_URL, {
+      method: "POST",
+      headers: { "content-type": "application/x-www-form-urlencoded" },
+      body,
+      cache: "no-store",
+    })
+    const data = (await res.json()) as { success?: boolean }
+    return data.success === true
+  } catch {
+    // Network / provider error — fail closed so a challenge can't be bypassed.
+    return false
+  }
+}