docs: overhaul README and mark project proprietary

- Rewrite README: accurate current feature set (public API, webhooks/Zapier,
  PayPal, accounting sync, e-sign, team, branding, inspections, maps, ~30 tables,
  4 cron jobs), emoji section headers, clearer setup and security sections.
- Remove the inline env-variable example block; point to .env.example / DIGITALOCEAN.md.
- Fix stale "local disk" storage references to DigitalOcean Spaces.
- License: change MIT -> Proprietary; add LICENSE file and package.json "UNLICENSED".

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

package.json

@@ -2,6 +2,7 @@
   "name": "property-management-network",
   "version": "0.1.0",
   "private": true,
+  "license": "UNLICENSED",
   "scripts": {
     "dev": "next dev",
     "build": "next build",