Add manual pension data entry and fix chart to use real historical data

- Add paste-and-preview modal for entering pension fund balances from bank website
- Backend upsert logic so n8n PDF uploads overwrite manual entries
- Chart now shows actual snapshot data with dynamic month labels
- New POST /pensions/manual endpoint for JSON-based fund entry

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/api.ts

@@ -269,11 +269,27 @@ export interface PensionSnapshot {
 
 export interface PensionUploadResult {
   imported: number;
+  updated: number;
   duplicates: number;
   errors: string[];
   snapshots: PensionSnapshot[];
 }
 
+export interface PensionManualEntry {
+  fund: string;
+  period_start: string;
+  period_end: string;
+  saldo_anterior: number;
+  aportes: number;
+  rendimientos: number;
+  retiros: number;
+  traslados: number;
+  comision: number;
+  correccion: number;
+  bonificacion: number;
+  saldo_final: number;
+}
+
 export const uploadPensionPDFs = (files: File[]) => {
   const form = new FormData();
   files.forEach((f) => form.append('files', f));
@@ -285,3 +301,6 @@ export const getPensionSnapshots = () =>
 
 export const getPensionFundSummary = () =>
   api.get<PensionSnapshot[]>('/pensions/fund-summary');
+
+export const submitPensionManualEntries = (entries: PensionManualEntry[]) =>
+  api.post<PensionUploadResult>('/pensions/manual', { entries });