chore: Move to Typescript (#2783)

This PR moves the entire project to Typescript. Due to the ~1000 ignores this will lead to a messy codebase for a while, but the churn is worth it – all of those ignore comments are places that were never type-safe previously.

closes #1282

server/mailer.test.ts

@@ -0,0 +1,25 @@
+import mailer from "./mailer";
+
+describe("Mailer", () => {
+  const fakeMailer = mailer;
+  // @ts-expect-error ts-migrate(7034) FIXME: Variable 'sendMailOutput' implicitly has type 'any... Remove this comment to see the full error message
+  let sendMailOutput;
+  beforeEach(() => {
+    process.env.URL = "http://localhost:3000";
+    process.env.SMTP_FROM_EMAIL = "hello@example.com";
+    jest.resetModules();
+    fakeMailer.transporter = {
+      // @ts-expect-error ts-migrate(7006) FIXME: Parameter 'output' implicitly has an 'any' type.
+      sendMail: (output) => (sendMailOutput = output),
+    };
+  });
+
+  test("#welcome", () => {
+    fakeMailer.welcome({
+      to: "user@example.com",
+      teamUrl: "http://example.com",
+    });
+    // @ts-expect-error ts-migrate(7005) FIXME: Variable 'sendMailOutput' implicitly has an 'any' ... Remove this comment to see the full error message
+    expect(sendMailOutput).toMatchSnapshot();
+  });
+});