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/random.ts

@@ -0,0 +1,19 @@
+export const randomEmail = () =>
+  `test_${Math.random().toString(36).substring(7)}@example.com`
+
+export const randomTeamName = () =>
+  `Team ${Math.random().toString(36).substring(7)}`
+
+export const randomPassword = () => `${Math.random().toString(36).substring(2)}`
+
+export const slugify = (text: string) =>
+  text
+    .toLowerCase()
+    .replace(/\s+/g, "-")
+    .replace(/[^\w-]+/g, "")
+
+export const randomItemTitle = () =>
+  `Item ${Math.random().toString(36).substring(7)}`
+
+export const randomItemDescription = () =>
+  `Description ${Math.random().toString(36).substring(7)}`