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/routes/email-signature.routes.js

@@ -0,0 +1,42 @@
+import express from 'express';
+import * as emailSignatureController from '../controllers/email-signature.controller.js';
+import { authenticate } from '../middlewares/auth/authMiddleware.js';
+import { validateBody } from '../middlewares/security/validateInput.js';
+import { z } from 'zod';
+
+const router = express.Router();
+
+// All routes require authentication
+router.use(authenticate);
+
+// Validation schemas
+const signatureSchema = z.object({
+  fullName: z.string().max(255).optional().or(z.literal('')).or(z.null()),
+  position: z.string().max(255).optional().or(z.literal('')).or(z.null()),
+  phone: z.string().max(50).optional().or(z.literal('')).or(z.null()),
+  email: z.string().email('Neplatný formát emailu').max(255).optional().or(z.literal('')).or(z.null()),
+  companyName: z.string().max(255).optional().or(z.literal('')).or(z.null()),
+  website: z.string().max(255).optional().or(z.literal('')).or(z.null()),
+  isEnabled: z.boolean().optional(),
+});
+
+const toggleSchema = z.object({
+  isEnabled: z.boolean(),
+});
+
+// Get user's signature
+router.get('/', emailSignatureController.getSignature);
+
+// Get formatted signature text
+router.get('/formatted', emailSignatureController.getFormattedSignature);
+
+// Create or update signature
+router.post('/', validateBody(signatureSchema), emailSignatureController.upsertSignature);
+
+// Toggle signature on/off
+router.patch('/toggle', validateBody(toggleSchema), emailSignatureController.toggleSignature);
+
+// Delete signature
+router.delete('/', emailSignatureController.deleteSignature);
+
+export default router;