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>

apps/Backend/src/services/networkSyncConfigService.ts

@@ -0,0 +1,58 @@
+import fs from "fs";
+import path from "path";
+import crypto from "crypto";
+
+const KEY_FILE = path.resolve(process.cwd(), "network-backup-key.json");
+const CONFIG_FILE = path.resolve(process.cwd(), "network-sync-config.json");
+
+export interface NetworkSyncConfig {
+  enabled: boolean;
+  syncHour: number;
+  sourceUrl: string;
+  apiKey: string;
+  lastSyncAt: string | null;
+  lastSyncStatus: string | null;
+  lastSyncError: string | null;
+}
+
+export function getOrCreateApiKey(): string {
+  if (fs.existsSync(KEY_FILE)) {
+    try {
+      const data = JSON.parse(fs.readFileSync(KEY_FILE, "utf8"));
+      if (data.apiKey) return data.apiKey;
+    } catch {}
+  }
+  const key = crypto.randomUUID();
+  fs.writeFileSync(KEY_FILE, JSON.stringify({ apiKey: key }), "utf8");
+  return key;
+}
+
+export function regenerateApiKey(): string {
+  const key = crypto.randomUUID();
+  fs.writeFileSync(KEY_FILE, JSON.stringify({ apiKey: key }), "utf8");
+  return key;
+}
+
+export function readSyncConfig(): NetworkSyncConfig {
+  if (fs.existsSync(CONFIG_FILE)) {
+    try {
+      return JSON.parse(fs.readFileSync(CONFIG_FILE, "utf8"));
+    } catch {}
+  }
+  return {
+    enabled: false,
+    syncHour: 0,
+    sourceUrl: "",
+    apiKey: "",
+    lastSyncAt: null,
+    lastSyncStatus: null,
+    lastSyncError: null,
+  };
+}
+
+export function writeSyncConfig(patch: Partial<NetworkSyncConfig>): NetworkSyncConfig {
+  const current = readSyncConfig();
+  const updated = { ...current, ...patch };
+  fs.writeFileSync(CONFIG_FILE, JSON.stringify(updated, null, 2), "utf8");
+  return updated;
+}