feat: ip_addersses.ip_address をユニークに（#229） (#237)

#229

Co-authored-by: miteruzo <miteruzo@naver.com>
Reviewed-on: https://git.miteruzo.com/miteruzo/btrc-hub/pulls/237

backend/db/migrate/20260126124100_add_unique_index_to_ip_addresses.rb

@@ -0,0 +1,3 @@
+class AddUniqueIndexToIpAddresses < ActiveRecord::Migration[8.0]
+  add_index :ip_addresses, :ip_address, unique: true, name: 'index_ip_addresses_on_ip_address'
+end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_01_21_225600) do
+ActiveRecord::Schema[8.0].define(version: 2026_01_26_124100) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -44,6 +44,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_01_21_225600) do
     t.boolean "banned", default: false, null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.index ["ip_address"], name: "index_ip_addresses_on_ip_address", unique: true
   end
 
   create_table "nico_tag_relations", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|