feat: add Drone CI pipelines, Jest unit tests, and Prettier check

Add Drone CI with server build/test and format check pipelines.
Add unit tests for password utils and recurrenceExpander.
Add check_format script, fix Jest config to ignore dist/,
remove dead CaldavService.test.ts, apply Prettier formatting.

apps/server/jest.config.js

@@ -1,4 +1,5 @@
 module.exports = {
   preset: "ts-jest",
   testEnvironment: "node",
+  testPathIgnorePatterns: ["/node_modules/", "/dist/"],
 };