feat: Add email signature feature

- Add email_signatures table to schema
- Add email signature service, controller, routes
- Users can create/edit signature in Profile
- Toggle to include signature when sending email replies

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/controllers/email-signature.controller.js

@@ -0,0 +1,93 @@
+import * as emailSignatureService from '../services/email-signature.service.js';
+
+/**
+ * Get current user's email signature
+ * GET /api/email-signature
+ */
+export const getSignature = async (req, res, next) => {
+  try {
+    const signature = await emailSignatureService.getSignature(req.userId);
+
+    res.status(200).json({
+      success: true,
+      data: signature,
+    });
+  } catch (error) {
+    next(error);
+  }
+};
+
+/**
+ * Create or update email signature
+ * POST /api/email-signature
+ */
+export const upsertSignature = async (req, res, next) => {
+  try {
+    const signature = await emailSignatureService.upsertSignature(req.userId, req.body);
+
+    res.status(200).json({
+      success: true,
+      data: signature,
+      message: 'Podpis bol uložený',
+    });
+  } catch (error) {
+    next(error);
+  }
+};
+
+/**
+ * Toggle signature on/off
+ * PATCH /api/email-signature/toggle
+ */
+export const toggleSignature = async (req, res, next) => {
+  try {
+    const { isEnabled } = req.body;
+    const signature = await emailSignatureService.toggleSignature(req.userId, isEnabled);
+
+    res.status(200).json({
+      success: true,
+      data: signature,
+      message: isEnabled ? 'Podpis zapnutý' : 'Podpis vypnutý',
+    });
+  } catch (error) {
+    next(error);
+  }
+};
+
+/**
+ * Get formatted signature text for email
+ * GET /api/email-signature/formatted
+ */
+export const getFormattedSignature = async (req, res, next) => {
+  try {
+    const signature = await emailSignatureService.getSignature(req.userId);
+    const formatted = emailSignatureService.formatSignatureText(signature);
+
+    res.status(200).json({
+      success: true,
+      data: {
+        text: formatted,
+        isEnabled: signature?.isEnabled || false,
+      },
+    });
+  } catch (error) {
+    next(error);
+  }
+};
+
+/**
+ * Delete email signature
+ * DELETE /api/email-signature
+ */
+export const deleteSignature = async (req, res, next) => {
+  try {
+    const result = await emailSignatureService.deleteSignature(req.userId);
+
+    res.status(200).json({
+      success: true,
+      message: result.message,
+    });
+  } catch (error) {
+    next(error);
+  }
+};