Deploy on DigitalOcean App Platform (GitHub-source build) + consolidate audit-fixes

Deploy config:
- .do/app.yaml: build the Dockerfile directly from GitHub (deploy_on_push) instead
  of a pre-built DOCR image; NEXT_PUBLIC_* set RUN_AND_BUILD_TIME with the
  propertymanagement.network domain so they bake into the client bundle; add
  custom domains block (apex + www); wire Sentry DSN (server + browser).

Included pending work from the audit-fixes branch:
- AI provider abstraction (OpenAI/Anthropic, admin-selectable; Anthropic default)
- Per-landlord e-signature (DocuSign OAuth + Dropbox Sign) + migration 0010
- Outbound webhooks / Zapier integration
- PayPal removal (Stripe-only billing)
- Storage hardening (fail-loud when Spaces unconfigured), security fixes

Verified: full production Docker build (same build-args as DO) passes clean.

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

lib/accounting/state.ts

@@ -1,22 +1,41 @@
 import crypto from "crypto"
 
-// Signed OAuth `state` (HMAC-SHA256) — carries the initiating owner + provider
-// and is tamper-proof, so the callback can't be forged/CSRF'd.
-const SECRET = process.env.BETTER_AUTH_SECRET ?? "dev-secret"
+// Signed OAuth `state` (HMAC-SHA256) — carries the initiating owner + provider,
+// a random nonce (bound to a cookie by the connect route for CSRF protection),
+// and an issued-at timestamp so a leaked state can't be replayed indefinitely.
 
-export function signState(data: { ownerId: string; provider: string }): string {
-  const payload = Buffer.from(JSON.stringify(data)).toString("base64url")
-  const sig = crypto.createHmac("sha256", SECRET).update(payload).digest("base64url")
+const STATE_TTL_MS = 10 * 60 * 1000 // 10 minutes
+
+// Short-lived httpOnly cookie the connect route sets and the callback verifies
+// against the state's nonce (binds the OAuth round-trip to the initiating browser).
+export const OAUTH_NONCE_COOKIE = "acct_oauth_nonce"
+
+// No insecure fallback: signing/verifying state without the real secret would
+// let anyone forge a state for any owner, so we fail closed (mirrors lib/crypto.ts).
+function secret(): string {
+  const s = process.env.BETTER_AUTH_SECRET
+  if (!s) throw new Error("BETTER_AUTH_SECRET is not set — required to sign OAuth state")
+  return s
+}
+
+export type OAuthState = { ownerId: string; provider: string; nonce: string }
+
+export function signState(data: OAuthState): string {
+  const payload = Buffer.from(JSON.stringify({ ...data, iat: Date.now() })).toString("base64url")
+  const sig = crypto.createHmac("sha256", secret()).update(payload).digest("base64url")
   return `${payload}.${sig}`
 }
 
-export function verifyState(state: string): { ownerId: string; provider: string } | null {
+export function verifyState(state: string): OAuthState | null {
   const [payload, sig] = state.split(".")
   if (!payload || !sig) return null
-  const expect = crypto.createHmac("sha256", SECRET).update(payload).digest("base64url")
+  const expect = crypto.createHmac("sha256", secret()).update(payload).digest("base64url")
   if (sig.length !== expect.length || !crypto.timingSafeEqual(Buffer.from(sig), Buffer.from(expect))) return null
   try {
-    return JSON.parse(Buffer.from(payload, "base64url").toString("utf8"))
+    const obj = JSON.parse(Buffer.from(payload, "base64url").toString("utf8")) as OAuthState & { iat?: number }
+    if (!obj.iat || Date.now() - obj.iat > STATE_TTL_MS) return null
+    if (!obj.ownerId || !obj.provider || !obj.nonce) return null
+    return { ownerId: obj.ownerId, provider: obj.provider, nonce: obj.nonce }
   } catch {
     return null
   }