支持已绑定设备追加 NFC 卡

- 新增已绑定设备追加卡会话和小程序入口

- 允许同设备多张 active 卡，保留 card_uuid 唯一并补齐老库迁移

- 收紧未知卡自动绑定和跨设备卡复用

验证：talkingq-url/.venv/bin/python -m pytest tests；compileall；npm run build:weapp

mini-program/database/init.sql

@@ -87,6 +87,8 @@ CREATE TABLE IF NOT EXISTS device_bind_sessions (
     max_attempt_count TINYINT UNSIGNED NOT NULL DEFAULT 5,
     attempt_count TINYINT UNSIGNED NOT NULL DEFAULT 0,
     status TINYINT NOT NULL DEFAULT 1,
+    bind_mode TINYINT NOT NULL DEFAULT 1,
+    card_uuid VARCHAR(64),
     confirmed_at DATETIME,
     consumed_at DATETIME,
     created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
@@ -111,7 +113,7 @@ CREATE TABLE IF NOT EXISTS device_bind_history (
 CREATE TABLE IF NOT EXISTS cards (
     card_id BIGINT PRIMARY KEY AUTO_INCREMENT,
     card_uuid VARCHAR(64) UNIQUE NOT NULL,
-    device_id VARCHAR(64) UNIQUE,
+    device_id VARCHAR(64),
     card_name VARCHAR(64),
     status TINYINT NOT NULL DEFAULT 0,
     total_swaps INT NOT NULL DEFAULT 0,