Vendor backend and frontend into the monorepo

The submodule collapse was only half applied: .gitmodules was deleted but
backend/ and frontend/ were still recorded as gitlinks, so none of their
files were tracked. Replace the gitlinks with the real trees.

Also untrack .env (it carried placeholder secrets) in favour of a tracked
.env.example, drop the committed __pycache__, and narrow the blanket *.png
ignore that would have swallowed design assets.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/tests/utils/user.ts

@@ -0,0 +1,35 @@
+import { expect, type Page } from "@playwright/test"
+
+export async function signUpNewUser(
+  page: Page,
+  name: string,
+  email: string,
+  password: string,
+) {
+  await page.goto("/signup")
+
+  await page.getByTestId("full-name-input").fill(name)
+  await page.getByTestId("email-input").fill(email)
+  await page.getByTestId("password-input").fill(password)
+  await page.getByTestId("confirm-password-input").fill(password)
+  await page.getByRole("button", { name: "Sign Up" }).click()
+  await page.goto("/login")
+}
+
+export async function logInUser(page: Page, email: string, password: string) {
+  await page.goto("/login")
+
+  await page.getByTestId("email-input").fill(email)
+  await page.getByTestId("password-input").fill(password)
+  await page.getByRole("button", { name: "Log In" }).click()
+  await page.waitForURL("/")
+  await expect(
+    page.getByText("Welcome back, nice to see you again!"),
+  ).toBeVisible()
+}
+
+export async function logOutUser(page: Page) {
+  await page.getByTestId("user-menu").click()
+  await page.getByRole("menuitem", { name: "Log out" }).click()
+  await page.goto("/login")
+}