feat: add Network Backup section to Database Management

PC2 can now automatically pull and restore a fresh copy of PC1's database
on a daily schedule. Config and API key are stored in local JSON files so
they survive database restores.

- New networkSyncConfigService: file-based config (network-backup-key.json,
  network-sync-config.json) that persists through DB restores
- New networkSyncService: streams live pg_dump from source PC over HTTP and
  pipes into psql, then reconnects Prisma and applies missing migrations
- 6 new endpoints: get/regenerate API key, serve backup stream (key-auth
  only), get/save sync config, trigger immediate sync
- Hourly cron job that fires only when current hour matches configured syncHour
- NetworkBackupManager component: shows this machine's key (show/copy/regen)
  and receiver config (enable toggle, hour picker 0-23, source URL + key,
  Save + Sync Now, last sync status)
- README setup guide for both PCs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/db/shared/.prisma-zod-generator-manifest.json

@@ -1,7 +1,7 @@
 {
   "version": "1.0",
   "generatorVersion": "1.0.0",
-  "generatedAt": "2026-06-06T04:01:46.483Z",
+  "generatedAt": "2026-06-09T04:01:43.616Z",
   "outputPath": "/home/ff/Desktop/DentalManagementMH06/packages/db/shared",
   "files": [
     "schemas/enums/TransactionIsolationLevel.schema.ts",