Add the management app: club-facing UI + real fee-payment tracking

Gives clubs a self-service /manage/ area for members, families, teams,
roles, and season memberships, alongside real fee-payment tracking
(FeePayment, record_payment/mark_as_paid/remaining_balance) so a
membership's paid status reflects actual money received instead of a
single manually-set flag.

management/pdf.py

@@ -0,0 +1,30 @@
+"""HTML-to-PDF rendering for exports (currently just the memberships list).
+
+Same lazy-import shape as billing.services.invoices.render_pdf -- WeasyPrint binds
+to native pango/cairo libraries, and a machine without them must still be able to
+run the app, the tests and every other page, so the import happens here, not at
+module scope, and only fails when someone actually asks for a PDF. Kept separate
+from billing's version rather than shared: the two exports have nothing else in
+common, and sharing would make one app depend on the other's error type for no
+real benefit.
+"""
+
+from django.template.loader import render_to_string
+
+
+class PDFExportError(Exception):
+    """Raised when WeasyPrint's native libraries aren't available."""
+
+
+def render_pdf(html: str) -> bytes:
+    try:
+        from weasyprint import HTML
+    except (ImportError, OSError) as error:
+        raise PDFExportError("PDF rendering needs the native pango/cairo libraries (on macOS: brew install pango).") from error
+
+    return HTML(string=html).write_pdf()
+
+
+def membership_list_pdf(context: dict) -> bytes:
+    html = render_to_string("management/membership_list_pdf.html", context)
+    return render_pdf(html)