fix: Improve bank/cash register display and exports

- Truncate explicatia field to 100 characters in table, Excel, and PDF exports
- Fix summary stats to separate opening balance from transactions:
  - Show Sold Precedent (from rows with null date)
  - Show Încasări and Plăți (only from actual transactions)
  - Show Sold Final (calculated correctly)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

reports-app/frontend/src/utils/exportUtils.js

@@ -477,6 +477,13 @@ export const exportBankCashRegisterPDF = (data, header, filename) => {
         .replace(/[ț]/gi, (m) => (m === m.toLowerCase() ? "t" : "T"));
     };
 
+    // Truncate text helper (limit explicatia to 100 chars)
+    const truncateText = (text, maxLength = 100) => {
+      if (!text) return "";
+      if (text.length <= maxLength) return text;
+      return text.substring(0, maxLength) + "...";
+    };
+
     // Group data by bank account (bancasa)
     const groupedByBank = {};
     const initialBalances = {};
@@ -696,7 +703,7 @@ export const exportBankCashRegisterPDF = (data, header, filename) => {
             tableRows.push([
               dateFormatted,
               row.nract || "",
-              removeDiacritics(row.explicatia || row.nume || ""),
+              truncateText(removeDiacritics(row.explicatia || row.nume || ""), 100),
               formatNumberForPDF(incasari),
               formatNumberForPDF(plati),
               formatNumberForPDF(row.sold),