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/openapi-ts.config.ts

@@ -0,0 +1,33 @@
+import { defineConfig } from "@hey-api/openapi-ts"
+
+export default defineConfig({
+  input: "./openapi.json",
+  output: "./src/client",
+
+  plugins: [
+    "legacy/axios",
+    {
+      name: "@hey-api/sdk",
+      // NOTE: this doesn't allow tree-shaking
+      asClass: true,
+      operationId: true,
+      classNameBuilder: "{{name}}Service",
+      methodNameBuilder: (operation) => {
+        // @ts-expect-error
+        let name: string = operation.name
+        // @ts-expect-error
+        const service: string = operation.service
+
+        if (service && name.toLowerCase().startsWith(service.toLowerCase())) {
+          name = name.slice(service.length)
+        }
+
+        return name.charAt(0).toLowerCase() + name.slice(1)
+      },
+    },
+    {
+      name: "@hey-api/schemas",
+      type: "json",
+    },
+  ],
+})