feat(contacts): switch contacts UX to email-first flow

- expose email in user search/contact responses

- add add-contact-by-email API endpoint

- show email in contacts/search and add contact form by email in Contacts tab

web/src/api/users.ts

@@ -48,6 +48,10 @@ export async function addContact(userId: number): Promise<void> {
   await http.post(`/users/${userId}/contacts`);
 }
 
+export async function addContactByEmail(email: string): Promise<void> {
+  await http.post("/users/contacts/by-email", { email });
+}
+
 export async function removeContact(userId: number): Promise<void> {
   await http.delete(`/users/${userId}/contacts`);
 }