feat(contacts): add contacts module with backend APIs and web tab

- add user_contacts table and migration

- expose /users/contacts list/add/remove endpoints

- add Contacts tab in chat list with add/remove actions

web/src/api/users.ts

@@ -38,3 +38,16 @@ export async function blockUser(userId: number): Promise<void> {
 export async function unblockUser(userId: number): Promise<void> {
   await http.delete(`/users/${userId}/block`);
 }
+
+export async function listContacts(): Promise<UserSearchItem[]> {
+  const { data } = await http.get<UserSearchItem[]>("/users/contacts");
+  return data;
+}
+
+export async function addContact(userId: number): Promise<void> {
+  await http.post(`/users/${userId}/contacts`);
+}
+
+export async function removeContact(userId: number): Promise<void> {
+  await http.delete(`/users/${userId}/contacts`);
+}