Add saved signature presets

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

app/src/app.js

@@ -5,7 +5,7 @@ const archiver = require('archiver');
 const PDFDocument = require('pdfkit');
 const QRCode = require('qrcode');
 const { pool, initializeDatabase } = require('./db');
-const { normalizeInvoiceData } = require('./invoice-data');
+const { isValidSignatureDataUrl, normalizeInvoiceData } = require('./invoice-data');
 
 const app = express();
 const sessionDurationMs = 1000 * 60 * 60 * 24 * 30;
@@ -362,6 +362,57 @@ app.delete('/api/payment-presets/:id', requireAuth, async (req, res, next) => {
     }
 });
 
+const signaturePresetResponse = (row) => ({
+    id: row.id,
+    name: row.name,
+    dataUrl: row.data_url
+});
+
+app.get('/api/signature-presets', requireAuth, async (req, res, next) => {
+    try {
+        const result = await pool.query(
+            'SELECT * FROM signature_presets WHERE user_id = $1 ORDER BY name',
+            [req.userId]
+        );
+        res.json({ presets: result.rows.map(signaturePresetResponse) });
+    } catch (error) {
+        next(error);
+    }
+});
+
+app.post('/api/signature-presets', requireAuth, async (req, res, next) => {
+    try {
+        const name = String(req.body.name || '').trim();
+        const dataUrl = req.body.dataUrl;
+        if (!name) {
+            res.status(400).json({ error: 'Zadejte název podpisu.' });
+            return;
+        }
+        if (!isValidSignatureDataUrl(dataUrl)) {
+            res.status(400).json({ error: 'Podpis musí být platný obrázek JPG nebo PNG.' });
+            return;
+        }
+        const result = await pool.query(`
+            INSERT INTO signature_presets (user_id, name, data_url)
+            VALUES ($1, $2, $3)
+            ON CONFLICT (user_id, name) DO UPDATE SET data_url = EXCLUDED.data_url
+            RETURNING *
+        `, [req.userId, name, dataUrl]);
+        res.status(201).json({ preset: signaturePresetResponse(result.rows[0]) });
+    } catch (error) {
+        next(error);
+    }
+});
+
+app.delete('/api/signature-presets/:id', requireAuth, async (req, res, next) => {
+    try {
+        await pool.query('DELETE FROM signature_presets WHERE id = $1 AND user_id = $2', [req.params.id, req.userId]);
+        res.status(204).end();
+    } catch (error) {
+        next(error);
+    }
+});
+
 const invoiceResponse = (row) => ({
     id: row.id,
     invoiceNumber: row.invoice_number,