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/ai/anthropic.ts

@@ -0,0 +1,15 @@
+import Anthropic from "@anthropic-ai/sdk"
+
+// Lazily construct the Anthropic client so `next build` does NOT require
+// ANTHROPIC_API_KEY — it's only needed at runtime when the admin selects the
+// Anthropic (Claude) provider for AI features. Mirrors lib/ai/client.ts.
+let _anthropic: Anthropic | null = null
+
+export function getAnthropic(): Anthropic {
+  if (!_anthropic) {
+    const key = process.env.ANTHROPIC_API_KEY
+    if (!key) throw new Error("ANTHROPIC_API_KEY is not set")
+    _anthropic = new Anthropic({ apiKey: key })
+  }
+  return _anthropic
+}