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/store/settingsStore.js

@@ -0,0 +1,51 @@
+"use client";
+
+import { create } from "zustand";
+import { CLIENT_STORE_TTL_MS } from "@/shared/constants/config";
+
+const useSettingsStore = create((set, get) => ({
+  settings: null,
+  loading: false,
+  error: null,
+  lastFetched: 0,
+
+  invalidate: () => set({ lastFetched: 0 }),
+
+  // Skips network when cache is fresh; pass {force:true} to override
+  fetchSettings: async ({ force = false } = {}) => {
+    const { lastFetched, settings } = get();
+    if (!force && settings && Date.now() - lastFetched < CLIENT_STORE_TTL_MS) return settings;
+    set({ loading: true, error: null });
+    try {
+      const res = await fetch("/api/settings");
+      const data = await res.json();
+      if (res.ok) {
+        set({ settings: data, loading: false, lastFetched: Date.now() });
+        return data;
+      }
+      set({ error: data.error, loading: false });
+    } catch (e) {
+      set({ error: "Failed to fetch settings", loading: false });
+    }
+    return null;
+  },
+
+  // PATCH server + merge into local cache (no extra fetch needed)
+  patchSettings: async (patch) => {
+    try {
+      const res = await fetch("/api/settings", {
+        method: "PATCH",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify(patch),
+      });
+      if (!res.ok) return null;
+      const updated = await res.json();
+      set({ settings: updated, lastFetched: Date.now() });
+      return updated;
+    } catch {
+      return null;
+    }
+  },
+}));
+
+export default useSettingsStore;