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/src/client/core/ApiRequestOptions.ts

@@ -0,0 +1,21 @@
+export type ApiRequestOptions<T = unknown> = {
+	readonly body?: any;
+	readonly cookies?: Record<string, unknown>;
+	readonly errors?: Record<number | string, string>;
+	readonly formData?: Record<string, unknown> | any[] | Blob | File;
+	readonly headers?: Record<string, unknown>;
+	readonly mediaType?: string;
+	readonly method:
+		| 'DELETE'
+		| 'GET'
+		| 'HEAD'
+		| 'OPTIONS'
+		| 'PATCH'
+		| 'POST'
+		| 'PUT';
+	readonly path?: Record<string, unknown>;
+	readonly query?: Record<string, unknown>;
+	readonly responseHeader?: string;
+	readonly responseTransformer?: (data: unknown) => Promise<T>;
+	readonly url: string;
+};