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/repos/settingsRepo.js

@@ -0,0 +1,98 @@
+import { getAdapter } from "../driver.js";
+import { parseJson, stringifyJson } from "../helpers/jsonCol.js";
+
+const DEFAULT_MITM_ROUTER_BASE = "http://127.0.0.1:20128";
+
+const DEFAULT_SETTINGS = {
+  cloudEnabled: false,
+  tunnelEnabled: false,
+  tunnelUrl: "",
+  tunnelProvider: "cloudflare",
+  tailscaleEnabled: false,
+  tailscaleUrl: "",
+  stickyRoundRobinLimit: 3,
+  providerStrategies: {},
+  comboStrategy: "fallback",
+  comboStickyRoundRobinLimit: 1,
+  comboStrategies: {},
+  requireLogin: true,
+  tunnelDashboardAccess: true,
+  enableObservability: true,
+  observabilityMaxRecords: 1000,
+  observabilityBatchSize: 20,
+  observabilityFlushIntervalMs: 5000,
+  observabilityMaxJsonSize: 5,
+  outboundProxyEnabled: false,
+  outboundProxyUrl: "",
+  outboundNoProxy: "",
+  mitmRouterBaseUrl: DEFAULT_MITM_ROUTER_BASE,
+  dnsToolEnabled: {},
+  rtkEnabled: true,
+  cavemanEnabled: false,
+  cavemanLevel: "full",
+};
+
+async function readRaw() {
+  const db = await getAdapter();
+  const row = db.get(`SELECT data FROM settings WHERE id = 1`);
+  return row ? parseJson(row.data, {}) : {};
+}
+
+// Merge raw settings with defaults; backward-compat for missing keys
+function mergeWithDefaults(raw) {
+  const merged = { ...DEFAULT_SETTINGS, ...(raw || {}) };
+  for (const [key, defVal] of Object.entries(DEFAULT_SETTINGS)) {
+    if (merged[key] === undefined) {
+      if (
+        key === "outboundProxyEnabled" &&
+        typeof merged.outboundProxyUrl === "string" &&
+        merged.outboundProxyUrl.trim()
+      ) {
+        merged[key] = true;
+      } else {
+        merged[key] = defVal;
+      }
+    }
+  }
+  return merged;
+}
+
+export async function getSettings() {
+  const raw = await readRaw();
+  return mergeWithDefaults(raw);
+}
+
+// Atomic read-merge-write inside transaction (prevents losing concurrent updates)
+export async function updateSettings(updates) {
+  const db = await getAdapter();
+  let next;
+  db.transaction(() => {
+    const row = db.get(`SELECT data FROM settings WHERE id = 1`);
+    const current = row ? parseJson(row.data, {}) : {};
+    next = { ...current, ...updates };
+    db.run(
+      `INSERT INTO settings(id, data) VALUES(1, ?) ON CONFLICT(id) DO UPDATE SET data = excluded.data`,
+      [stringifyJson(next)]
+    );
+  });
+  return mergeWithDefaults(next);
+}
+
+export async function isCloudEnabled() {
+  const settings = await getSettings();
+  return settings.cloudEnabled === true;
+}
+
+export async function getCloudUrl() {
+  const settings = await getSettings();
+  return (
+    settings.cloudUrl ||
+    process.env.CLOUD_URL ||
+    process.env.NEXT_PUBLIC_CLOUD_URL ||
+    ""
+  );
+}
+
+export async function exportSettings() {
+  return await readRaw();
+}