feat(server/db): 多库(3/4)— Dialect 抽象(upsert/锁)+ 合并 directory_version

- db.Dialect:LockForUpdate(mysql "FOR UPDATE" / sqlite "")、Upsert(中性
  EXCLUDED.col → mysql VALUES()/ sqlite excluded.);DialectForDB 从连接驱动推导
- 9 处 ON DUPLICATE KEY、11 处 FOR UPDATE 全走 dialect;sqlite 靠 _txlock=
  immediate 取得 BEGIN IMMEDIATE 悲观锁等价语义
- directory_version 三处重复合并为 store.BumpDirectoryVersion(dialect 感知)
- 这些文件同时含(2/4)的 UTC→Go 改动(与 upsert/锁同语句交错,无法拆分)
- 顺带:usage 的 FIELD()、codes 的 DATE_ADD/GREATEST 续期、nodes 的
  UNIX_TIMESTAMP、NULLIF 等 MySQL 专属构造一并退回 Go/可移植写法

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

server/internal/usage/store.go

@@ -5,6 +5,8 @@ import (
 	"database/sql"
 	"fmt"
 	"time"
+
+	dbx "github.com/wangjia/pangolin/server/internal/db"
 )
 
 // Unlimited is the sentinel returned by CheckFreeConnect for plans with no
@@ -37,11 +39,12 @@ type DailyUsage struct {
 // Store wraps a *sql.DB and exposes the usage_daily / plans / users queries the
 // usage package needs.
 type Store struct {
-	db *sql.DB
+	db      *sql.DB
+	dialect dbx.Dialect
 }
 
-// NewStore creates a Store backed by the given MySQL connection pool.
-func NewStore(db *sql.DB) *Store { return &Store{db: db} }
+// NewStore creates a Store backed by the given connection pool (MySQL or SQLite).
+func NewStore(db *sql.DB) *Store { return &Store{db: db, dialect: dbx.DialectForDB(db)} }
 
 // AggregateUsage accumulates one usage delta into usage_daily for (userID, day)
 // using INSERT … ON DUPLICATE KEY UPDATE so concurrent reports from multiple
@@ -51,10 +54,10 @@ func (s *Store) AggregateUsage(ctx context.Context, userID int64, day time.Time,
 	_, err := s.db.ExecContext(ctx,
 		`INSERT INTO usage_daily (user_id, date, bytes_up, bytes_down, minutes_used)
 		 VALUES (?, ?, ?, ?, ?)
-		 ON DUPLICATE KEY UPDATE
-		   bytes_up     = bytes_up     + VALUES(bytes_up),
-		   bytes_down   = bytes_down   + VALUES(bytes_down),
-		   minutes_used = minutes_used + VALUES(minutes_used)`,
+		 `+s.dialect.Upsert([]string{"user_id", "date"},
+			"bytes_up = bytes_up + EXCLUDED.bytes_up",
+			"bytes_down = bytes_down + EXCLUDED.bytes_down",
+			"minutes_used = minutes_used + EXCLUDED.minutes_used"),
 		userID, d, bytesUp, bytesDown, minutes)
 	if err != nil {
 		return fmt.Errorf("store.AggregateUsage: %w", err)
@@ -128,6 +131,7 @@ func (s *Store) GetDay(ctx context.Context, userID int64, day time.Time) (*Daily
 // SELECT … FOR UPDATE to be safe under concurrent unlock attempts.
 func (s *Store) MarkAdUnlocked(ctx context.Context, userID int64, day time.Time) (alreadyUnlocked bool, err error) {
 	d := day.UTC().Format(dateLayout)
+	now := time.Now().UTC()
 
 	tx, err := s.db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelReadCommitted})
 	if err != nil {
@@ -142,7 +146,7 @@ func (s *Store) MarkAdUnlocked(ctx context.Context, userID int64, day time.Time)
 
 	var unlockedAt sql.NullTime
 	row := tx.QueryRowContext(ctx,
-		`SELECT ad_unlocked_at FROM usage_daily WHERE user_id = ? AND date = ? FOR UPDATE`,
+		`SELECT ad_unlocked_at FROM usage_daily WHERE user_id = ? AND date = ? `+s.dialect.LockForUpdate(),
 		userID, d)
 	switch err := row.Scan(&unlockedAt); err {
 	case nil:
@@ -155,16 +159,16 @@ func (s *Store) MarkAdUnlocked(ctx context.Context, userID int64, day time.Time)
 			return true, nil
 		}
 		if _, uErr := tx.ExecContext(ctx,
-			`UPDATE usage_daily SET ad_unlocked_at = UTC_TIMESTAMP(6)
+			`UPDATE usage_daily SET ad_unlocked_at = ?
 			 WHERE user_id = ? AND date = ? AND ad_unlocked_at IS NULL`,
-			userID, d); uErr != nil {
+			now, userID, d); uErr != nil {
 			return false, fmt.Errorf("store.MarkAdUnlocked update: %w", uErr)
 		}
 	case sql.ErrNoRows:
 		if _, iErr := tx.ExecContext(ctx,
 			`INSERT INTO usage_daily (user_id, date, ad_unlocked_at)
-			 VALUES (?, ?, UTC_TIMESTAMP(6))`,
-			userID, d); iErr != nil {
+			 VALUES (?, ?, ?)`,
+			userID, d, now); iErr != nil {
 			return false, fmt.Errorf("store.MarkAdUnlocked insert: %w", iErr)
 		}
 	default:
@@ -187,10 +191,11 @@ func (s *Store) EffectivePlan(ctx context.Context, userID int64) (*Plan, error)
 		`SELECT p.code, p.daily_minutes, p.ad_gate
 		 FROM subscriptions s
 		 JOIN plans p ON p.id = s.plan_id
-		 WHERE s.user_id = ? AND s.expires_at > UTC_TIMESTAMP(6)
-		 ORDER BY FIELD(p.code, 'team', 'pro', 'free'), s.expires_at DESC
+		 WHERE s.user_id = ? AND s.expires_at > ?
+		 ORDER BY CASE p.code WHEN 'team' THEN 0 WHEN 'pro' THEN 1 WHEN 'free' THEN 2 ELSE 3 END,
+		          s.expires_at DESC
 		 LIMIT 1`,
-		userID).Scan(&p.Code, &p.DailyMinutes, &p.AdGate)
+		userID, time.Now().UTC()).Scan(&p.Code, &p.DailyMinutes, &p.AdGate)
 	if err == nil {
 		return &p, nil
 	}