Pension assumptions editable + dirty-form guard + empty-state CTA

Per-fund contribution and annual-rate assumptions are now editable in a
Supuestos dialog on Pensiones and persisted server-side in UserSettings
so projections survive devices and reloads; saldo inicial keeps coming
from the latest snapshot (UX-12). The recurring-item dialog confirms
before discarding unsaved edits, with the dirty baseline computed from
the same values the populate effect sets (UX-06). Empty transaction
lists now offer an inline add button (UX-14).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/lib/api.ts

@@ -518,3 +518,15 @@ export interface SyncStatusResponse {
 }
 
 export const getSyncStatus = () => api.get<SyncStatusResponse>('/sync-status/');
+
+// --- User Settings ---
+
+export type UserSettingsData = Record<string, unknown>;
+
+export interface UserSettingsRead {
+  key: string;
+  data: UserSettingsData;
+  updated_at: string;
+}
+
+export const getUserSettings = () => api.get<UserSettingsRead>('/settings/');