feat(db): migrate from lowdb to SQLite with repos pattern

- Add modular DB layer (adapters, migrations, repos, helpers)
- Replace localDb/usageDb/requestDetailsDb monoliths with repos
- Add Tailscale tunnel integration & status check API
- Add /api/cli-tools/all-statuses aggregated endpoint
- Add settingsStore (Zustand) and mitm/dbReader
- Add DB unit tests (benchmark, concurrent, migration, vs-lowdb)

src/lib/db/backup.js

@@ -0,0 +1,35 @@
+import fs from "node:fs";
+import path from "node:path";
+import { BACKUPS_DIR, ensureDirs } from "./paths.js";
+import { timestampSlug, getAppVersion } from "./version.js";
+
+const KEEP_BACKUPS = 5;
+
+export function makeBackupDir(label) {
+  ensureDirs();
+  const ver = getAppVersion();
+  const slug = `${label}-${ver}-${timestampSlug()}`;
+  const dir = path.join(BACKUPS_DIR, slug);
+  fs.mkdirSync(dir, { recursive: true });
+  return dir;
+}
+
+export function backupFile(srcPath, destDir, destName = null) {
+  if (!fs.existsSync(srcPath)) return null;
+  const name = destName || path.basename(srcPath);
+  const dest = path.join(destDir, name);
+  fs.copyFileSync(srcPath, dest);
+  return dest;
+}
+
+export function pruneOldBackups() {
+  if (!fs.existsSync(BACKUPS_DIR)) return;
+  const entries = fs.readdirSync(BACKUPS_DIR, { withFileTypes: true })
+    .filter((e) => e.isDirectory())
+    .map((e) => ({ name: e.name, full: path.join(BACKUPS_DIR, e.name), mtime: fs.statSync(path.join(BACKUPS_DIR, e.name)).mtimeMs }))
+    .sort((a, b) => b.mtime - a.mtime);
+
+  for (const old of entries.slice(KEEP_BACKUPS)) {
+    try { fs.rmSync(old.full, { recursive: true, force: true }); } catch {}
+  }
+}