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>

app/(auth)/login/page.tsx

@@ -1,8 +1,14 @@
+import type { Metadata } from "next"
 import Link from "next/link"
 import { Logo } from "@/components/shared/logo"
 import { TurnstileWidget } from "@/components/shared/turnstile-widget"
 import { signIn, signInWithGoogle } from "@/app/actions/auth"
 
+export const metadata: Metadata = {
+  title: "Sign in",
+  robots: { index: false, follow: true },
+}
+
 export default async function LoginPage({
   searchParams,
 }: {