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/db/schema.js

@@ -310,6 +310,21 @@ export const services = pgTable('services', {
   updatedAt: timestamp('updated_at').defaultNow().notNull(),
 });
 
+// Email Signatures table - email podpisy používateľov
+export const emailSignatures = pgTable('email_signatures', {
+  id: uuid('id').primaryKey().defaultRandom(),
+  userId: uuid('user_id').references(() => users.id, { onDelete: 'cascade' }).notNull().unique(),
+  fullName: text('full_name'),
+  position: text('position'),
+  phone: text('phone'),
+  email: text('email'),
+  companyName: text('company_name'),
+  website: text('website'),
+  isEnabled: boolean('is_enabled').default(true).notNull(),
+  createdAt: timestamp('created_at').defaultNow().notNull(),
+  updatedAt: timestamp('updated_at').defaultNow().notNull(),
+});
+
 // Messages table - interná komunikácia medzi používateľmi
 export const messages = pgTable('messages', {
   id: uuid('id').primaryKey().defaultRandom(),