feat(auth): 验证码/注册/登录/JWT 鉴权模块 (tsk_2PFfyviECIXh)

实现 server/internal/auth 控制面鉴权底座，对应 doc/02 §4.1、doc/06 §3：

- POST /v1/auth/code：IP+邮箱双维度 Redis 滑窗限频（同邮箱 1/min、同 IP 10/h）
  + 一次性邮箱域黑名单（embed 词表）→ 6 位数字码写 auth:code:{email} TTL 10min
  → 异步发信（SMTP / 开发态 log mailer）。
- POST /v1/auth/register：验码（一次性，删 key；超次数烧码）→ 单事务建号
  （uuid + dp_uuid 应用层生成、argon2id）+ 7 天 PRO 试用（source='trial'）→ 签发 JWT。
- POST /v1/auth/login：argon2id 校验（失败恒定时、未知用户走 dummy hash）；
  失败计数限流 rl:login:{email} + 锁定；banned 拒绝。
- POST /v1/auth/refresh：RS256，access 15min + refresh 30d 落 Redis 白名单
  jwt:refresh:{jti}，旋转时删旧写新；JWT 头带 kid，验证端接受新旧公钥支持轮换。
- RequireAuth 中间件：解析 Bearer access，注入 user id（复用 codes.CtxKeyUserID
  避免循环依赖）+ uuid + claims 到 context。
- 错误体统一走 internal/apierr 的 {code, message_zh, message_en}，文案双语脱敏。
- 文件拆分：handler/service/password/token/ratelimit/emailcheck/store/mailer/
  middleware/errors/keyloader；config 增加可选 JWT PEM 路径/kid 加载。

测试：password/token/ratelimit/emailcheck/service/handler/middleware 单测
（miniredis，含注册全流程、重复邮箱 409、验证码错误/过期/复用/烧码、限频 429
带 Retry-After、登录失败锁定、banned 拒绝、refresh 旋转后旧 token 失效），
go test -race 通过；集成测试 integration_test.go（testcontainers MySQL8+Redis，
register→login→refresh→受保护接口全链路，构建 tag integration）与 codes 模块同构。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/internal/auth/keyloader.go

@@ -0,0 +1,49 @@
+package auth
+
+import (
+	"crypto/rsa"
+	"fmt"
+	"os"
+)
+
+// LoadTokenConfig assembles a TokenConfig from PEM files on disk: one private
+// signing key (privateKeyPath, identified by signKID) and a set of public keys
+// (publicKeyPaths: kid -> path) accepted for verification, supporting key
+// rotation. The signing key's public part is added automatically if its kid is
+// absent from publicKeyPaths.
+func LoadTokenConfig(privateKeyPath, signKID string, publicKeyPaths map[string]string) (TokenConfig, error) {
+	if privateKeyPath == "" {
+		return TokenConfig{}, fmt.Errorf("auth: JWT private key path is empty")
+	}
+	if signKID == "" {
+		return TokenConfig{}, fmt.Errorf("auth: JWT key id (kid) is empty")
+	}
+
+	privPEM, err := os.ReadFile(privateKeyPath)
+	if err != nil {
+		return TokenConfig{}, fmt.Errorf("auth: read private key: %w", err)
+	}
+	priv, err := LoadPrivateKeyPEM(privPEM)
+	if err != nil {
+		return TokenConfig{}, err
+	}
+
+	verify := map[string]*rsa.PublicKey{}
+	for kid, path := range publicKeyPaths {
+		pubPEM, err := os.ReadFile(path)
+		if err != nil {
+			return TokenConfig{}, fmt.Errorf("auth: read public key %q: %w", kid, err)
+		}
+		pub, err := LoadPublicKeyPEM(pubPEM)
+		if err != nil {
+			return TokenConfig{}, fmt.Errorf("auth: parse public key %q: %w", kid, err)
+		}
+		verify[kid] = pub
+	}
+
+	return TokenConfig{
+		SignKey:    priv,
+		SignKID:    signKID,
+		VerifyKeys: verify,
+	}, nil
+}