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/driver.js

@@ -0,0 +1,52 @@
+import { ensureDirs, DATA_FILE } from "./paths.js";
+
+// Use global to survive Next.js dev hot-reload (module state resets on reload)
+if (!global._dbAdapter) global._dbAdapter = { instance: null, initPromise: null, logged: false };
+const state = global._dbAdapter;
+
+async function tryBetterSqlite() {
+  try {
+    const { createBetterSqliteAdapter } = await import("./adapters/betterSqliteAdapter.js");
+    return createBetterSqliteAdapter(DATA_FILE);
+  } catch (e) {
+    console.warn(`[DB] better-sqlite3 unavailable: ${e.message}`);
+    return null;
+  }
+}
+
+async function trySqlJs() {
+  try {
+    const { createSqlJsAdapter } = await import("./adapters/sqljsAdapter.js");
+    return await createSqlJsAdapter(DATA_FILE);
+  } catch (e) {
+    console.warn(`[DB] sql.js unavailable: ${e.message}`);
+    return null;
+  }
+}
+
+async function initAdapter() {
+  ensureDirs();
+  let adapter = await tryBetterSqlite();
+  if (!adapter) adapter = await trySqlJs();
+  if (!adapter) throw new Error("[DB] No SQLite driver available (better-sqlite3 + sql.js both failed)");
+
+  if (!state.logged) {
+    console.log(`[DB] Driver: ${adapter.driver} | file: ${DATA_FILE}`);
+    state.logged = true;
+  }
+
+  const { runMigrationOnce } = await import("./migrate.js");
+  await runMigrationOnce(adapter);
+  return adapter;
+}
+
+export async function getAdapter() {
+  if (state.instance) return state.instance;
+  if (!state.initPromise) state.initPromise = initAdapter().then((a) => { state.instance = a; return a; });
+  return state.initPromise;
+}
+
+export function getAdapterSync() {
+  if (!state.instance) throw new Error("[DB] adapter not initialized — await getAdapter() first");
+  return state.instance;
+}