feat: Add company linking to personal contacts

- Add companyId column to personal_contacts table
- Update personal-contact service to include companyName in list
- Add getContactsByCompanyId function for company contacts endpoint
- Add GET /companies/:companyId/contacts endpoint
- Add companyId to contact validation schema

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

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

src/db/schema.js

@@ -79,10 +79,11 @@ export const contacts = pgTable('contacts', {
   accountEmailUnique: unique('account_email_unique').on(table.emailAccountId, table.email),
 }));
 
-// Personal contacts - osobné kontakty používateľa (bez väzby na firmu alebo email account)
+// Personal contacts - osobné kontakty používateľa (s voliteľnou väzbou na firmu)
 export const personalContacts = pgTable('personal_contacts', {
   id: uuid('id').primaryKey().defaultRandom(),
   userId: uuid('user_id').references(() => users.id, { onDelete: 'cascade' }).notNull(),
+  companyId: uuid('company_id').references(() => companies.id, { onDelete: 'set null' }), // voliteľná väzba na firmu
   firstName: text('first_name').notNull(),
   lastName: text('last_name'),
   phone: text('phone').notNull(),