feat: add OpenAPI doc for update_profile_fields endpoint

Add ProfileFieldDto and UpdateProfileFieldsRequest to api-types,
annotate update_profile_fields_handler with utoipa::path, register
in UsersDoc. Coverage now 100%.

crates/api-types/src/users.rs

@@ -83,3 +83,14 @@ pub struct ProfileResponse {
     pub bio: Option<String>,
     pub avatar_url: Option<String>,
 }
+
+#[derive(Debug, Clone, Serialize, Deserialize, utoipa::ToSchema)]
+pub struct ProfileFieldDto {
+    pub name: String,
+    pub value: String,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, utoipa::ToSchema)]
+pub struct UpdateProfileFieldsRequest {
+    pub fields: Vec<ProfileFieldDto>,
+}