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/plan-limits.ts

@@ -0,0 +1,41 @@
+import { eq } from "drizzle-orm"
+import { db } from "@/lib/db"
+import { profiles } from "@/lib/db/schema"
+import { PLAN_LIMITS } from "@/lib/stripe/plans"
+import { getUserStorageBytes } from "@/lib/storage"
+import type { Plan } from "@/types"
+
+/**
+ * Server-side plan-limit enforcement helpers. Single source of truth is
+ * PLAN_LIMITS in lib/stripe/plans.ts — never hardcode limit numbers in routes.
+ */
+
+/** The user's current plan (defaults to "starter" if no profile row). */
+export async function getUserPlan(userId: string): Promise<Plan> {
+  const profile = await db.query.profiles.findFirst({
+    where: eq(profiles.id, userId),
+    columns: { plan: true },
+  })
+  return (profile?.plan ?? "starter") as Plan
+}
+
+/**
+ * Returns an error message if storing `incomingBytes` more would exceed the
+ * user's plan storage cap, otherwise null. Reads actual usage from the storage
+ * backend so it stays accurate regardless of which tables reference the files.
+ */
+export async function checkStorageLimit(
+  userId: string,
+  incomingBytes: number
+): Promise<string | null> {
+  const plan = await getUserPlan(userId)
+  const maxBytes = PLAN_LIMITS[plan].maxStorageMB * 1024 * 1024
+  if (!Number.isFinite(maxBytes)) return null // unlimited plan
+
+  const used = await getUserStorageBytes(userId)
+  if (used + incomingBytes > maxBytes) {
+    const limitMb = PLAN_LIMITS[plan].maxStorageMB
+    return `Storage limit reached (${limitMb} MB on your plan). Upgrade for more space.`
+  }
+  return null
+}