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)

tests/unit/db-migration-chain.test.js

@@ -0,0 +1,100 @@
+// Verify schema migration chain runs correctly across versions.
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
+
+let tempDir;
+const originalDataDir = process.env.DATA_DIR;
+
+beforeEach(() => {
+  tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "9router-mig-"));
+  process.env.DATA_DIR = tempDir;
+  // Reset global singleton so each test gets fresh adapter pointed at tempDir
+  delete global._dbAdapter;
+  vi.resetModules();
+});
+
+afterEach(() => {
+  // Close adapter to release file handles before rm
+  try { global._dbAdapter?.instance?.close?.(); } catch {}
+  delete global._dbAdapter;
+  if (tempDir) fs.rmSync(tempDir, { recursive: true, force: true });
+  if (originalDataDir === undefined) delete process.env.DATA_DIR;
+  else process.env.DATA_DIR = originalDataDir;
+});
+
+describe("Schema migrations", () => {
+  it("fresh DB → applies migrations & stamps schemaVersion", async () => {
+    const { getAdapter } = await import("@/lib/db/driver.js");
+    const { latestVersion } = await import("@/lib/db/migrations/index.js");
+    const db = await getAdapter();
+    const row = db.get(`SELECT value FROM _meta WHERE key='schemaVersion'`);
+    expect(parseInt(row.value, 10)).toBe(latestVersion());
+
+    const tables = db.all(`SELECT name FROM sqlite_master WHERE type='table'`).map(t => t.name);
+    expect(tables).toEqual(expect.arrayContaining([
+      "_meta", "settings", "providerConnections", "providerNodes",
+      "proxyPools", "apiKeys", "combos", "kv", "usageHistory", "usageDaily", "requestDetails",
+    ]));
+  });
+
+  it("existing DB at older schemaVersion → re-applies pending migrations on restart", async () => {
+    // 1st boot
+    const { getAdapter } = await import("@/lib/db/driver.js");
+    const db = await getAdapter();
+    db.run(`INSERT INTO settings(id, data) VALUES(1, ?) ON CONFLICT(id) DO UPDATE SET data = excluded.data`, ['{"foo":"bar"}']);
+    db.run(`UPDATE _meta SET value = '0' WHERE key = 'schemaVersion'`);
+    db.close?.();
+
+    // 2nd boot: full reset to simulate process restart
+    delete global._dbAdapter;
+    vi.resetModules();
+    const { getAdapter: getAdapter2 } = await import("@/lib/db/driver.js");
+    const { latestVersion } = await import("@/lib/db/migrations/index.js");
+    const db2 = await getAdapter2();
+    const row = db2.get(`SELECT value FROM _meta WHERE key='schemaVersion'`);
+    expect(parseInt(row.value, 10)).toBe(latestVersion());
+
+    const settings = db2.get(`SELECT data FROM settings WHERE id=1`);
+    expect(JSON.parse(settings.data)).toEqual({ foo: "bar" });
+  });
+
+  it("fresh DB + legacy db.json → imports data automatically", async () => {
+    // Simulate user upgrading: place legacy JSON in DATA_DIR before first boot
+    const legacy = {
+      settings: { foo: "legacy-value" },
+      apiKeys: [{ id: "k1", key: "abc", name: "test", createdAt: new Date().toISOString() }],
+      modelAliases: { "gpt-4": "gpt-4-turbo" },
+    };
+    fs.writeFileSync(path.join(tempDir, "db.json"), JSON.stringify(legacy));
+
+    const { getAdapter } = await import("@/lib/db/driver.js");
+    const db = await getAdapter();
+
+    const settings = db.get(`SELECT data FROM settings WHERE id=1`);
+    expect(JSON.parse(settings.data)).toEqual({ foo: "legacy-value" });
+
+    const keys = db.all(`SELECT * FROM apiKeys`);
+    expect(keys).toHaveLength(1);
+    expect(keys[0].key).toBe("abc");
+
+    const aliases = db.all(`SELECT * FROM kv WHERE scope='modelAliases'`);
+    expect(aliases).toHaveLength(1);
+  });
+
+  it("auto-sync re-creates missing index when DB lacks it", async () => {
+    const { getAdapter } = await import("@/lib/db/driver.js");
+    const db = await getAdapter();
+    db.exec(`DROP INDEX IF EXISTS idx_pn_type`);
+    expect(db.all(`PRAGMA index_list(providerNodes)`).map(i => i.name)).not.toContain("idx_pn_type");
+    db.close?.();
+
+    delete global._dbAdapter;
+    vi.resetModules();
+    const { getAdapter: getAdapter2 } = await import("@/lib/db/driver.js");
+    const db2 = await getAdapter2();
+    const idx = db2.all(`PRAGMA index_list(providerNodes)`).map(i => i.name);
+    expect(idx).toContain("idx_pn_type");
+  });
+});