Add comprehensive test suite with CI workflow

- 211 tests across 15 files covering services (tracking, discovery,
  metadata, backup, credits, webhooks, settings, update-check, colors,
  person), utilities (config, cron, providers, title-theme), and TMDB
  image URL helpers
- `lib/test-preload.ts` + `bunfig.toml` wire up a global in-memory
  SQLite DB with migrations for all DB-backed tests
- `lib/test-utils.ts` provides `clearAllTables()` and seed helpers
  (insertUser, insertTitle, insertTvShow, insertMovieWatch, etc.)
- Export `getBackupSource`, `isKnownBackup`, `isValidBackupFilename`,
  `buildBackupCron`, `performUpdateCheck` internals for direct testing
- GitHub Actions workflow runs `bun test --coverage` on push/PR to main

lib/services/settings.test.ts

@@ -0,0 +1,70 @@
+import { beforeEach, describe, expect, test } from "bun:test";
+import { clearAllTables, insertUser } from "@/lib/test-utils";
+import {
+  getSetting,
+  getUserCount,
+  isRegistrationOpen,
+  setSetting,
+} from "./settings";
+
+beforeEach(() => {
+  clearAllTables();
+});
+
+// ── getSetting / setSetting ─────────────────────────────────────────
+
+describe("getSetting / setSetting", () => {
+  test("returns null for missing key", () => {
+    expect(getSetting("nonexistent")).toBeNull();
+  });
+
+  test("stores and retrieves a value", () => {
+    setSetting("theme", "dark");
+    expect(getSetting("theme")).toBe("dark");
+  });
+
+  test("upserts: overwrites existing value", () => {
+    setSetting("theme", "dark");
+    setSetting("theme", "light");
+    expect(getSetting("theme")).toBe("light");
+  });
+});
+
+// ── getUserCount ────────────────────────────────────────────────────
+
+describe("getUserCount", () => {
+  test("returns 0 when no users", () => {
+    expect(getUserCount()).toBe(0);
+  });
+
+  test("returns correct count", () => {
+    insertUser("user-1");
+    insertUser("user-2");
+    expect(getUserCount()).toBe(2);
+  });
+});
+
+// ── isRegistrationOpen ──────────────────────────────────────────────
+
+describe("isRegistrationOpen", () => {
+  test("returns true when no users exist (first-run)", () => {
+    expect(isRegistrationOpen()).toBe(true);
+  });
+
+  test("returns false when users exist and setting is not set", () => {
+    insertUser();
+    expect(isRegistrationOpen()).toBe(false);
+  });
+
+  test("returns true when users exist and setting is 'true'", () => {
+    insertUser();
+    setSetting("registrationOpen", "true");
+    expect(isRegistrationOpen()).toBe(true);
+  });
+
+  test("returns false when users exist and setting is 'false'", () => {
+    insertUser();
+    setSetting("registrationOpen", "false");
+    expect(isRegistrationOpen()).toBe(false);
+  });
+});