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/src/utils/password.test.ts

@@ -0,0 +1,37 @@
+import { hash, compare } from "./password";
+
+describe("password", () => {
+  describe("hash()", () => {
+    it("returns a valid bcrypt hash", async () => {
+      const result = await hash("testpassword");
+      expect(result).toMatch(/^\$2b\$/);
+    });
+
+    it("produces different hashes for the same password (salt)", async () => {
+      const hash1 = await hash("samepassword");
+      const hash2 = await hash("samepassword");
+      expect(hash1).not.toBe(hash2);
+    });
+  });
+
+  describe("compare()", () => {
+    it("returns true for the correct password", async () => {
+      const hashed = await hash("correct");
+      const result = await compare("correct", hashed);
+      expect(result).toBe(true);
+    });
+
+    it("returns false for a wrong password", async () => {
+      const hashed = await hash("correct");
+      const result = await compare("wrong", hashed);
+      expect(result).toBe(false);
+    });
+
+    it("handles special characters and unicode", async () => {
+      const password = "p@$$w0rd!#%& äöü 🔑";
+      const hashed = await hash(password);
+      expect(await compare(password, hashed)).toBe(true);
+      expect(await compare("other", hashed)).toBe(false);
+    });
+  });
+});