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/(admin)/admin/system/page.tsx

@@ -1,6 +1,8 @@
 import { getSystemCounts, getEnvHealth } from "@/lib/db/admin-queries"
 import { getMaintenanceMode } from "@/lib/settings"
+import { aiProviderStatus } from "@/lib/ai/provider"
 import { MaintenanceToggle } from "@/components/admin/maintenance-toggle"
+import { AiProviderToggle } from "@/components/admin/ai-provider-toggle"
 import { formatDate } from "@/lib/utils"
 import { Settings, Database, Table2 } from "lucide-react"
 
@@ -13,10 +15,11 @@ function humanize(name: string): string {
 }
 
 export default async function AdminSystemPage() {
-  const [{ counts, cronLastRun }, env, maintenance] = await Promise.all([
+  const [{ counts, cronLastRun }, env, maintenance, aiProvider] = await Promise.all([
     getSystemCounts(),
     Promise.resolve(getEnvHealth()),
     getMaintenanceMode(),
+    aiProviderStatus(),
   ])
 
   return (
@@ -37,6 +40,18 @@ export default async function AdminSystemPage() {
         />
       </div>
 
+      {/* AI provider selection */}
+      <div className="mb-5">
+        <AiProviderToggle
+          selected={aiProvider.selected}
+          effective={aiProvider.effective}
+          openaiConfigured={aiProvider.openaiConfigured}
+          anthropicConfigured={aiProvider.anthropicConfigured}
+          openaiModel={aiProvider.openaiModel}
+          anthropicModel={aiProvider.anthropicModel}
+        />
+      </div>
+
       <div className="grid grid-cols-1 lg:grid-cols-2 gap-4 sm:gap-5 mb-5">
         {/* ── Environment configuration ───────────────────────────────── */}
         <div className="rounded-2xl border border-white/[0.06] bg-[#16161f] overflow-hidden">