feat(server): 免费版账户级分钟卡控 + 累加式看广告加时(#21 后端)

免费版此前形同虚设:ConnectNode 每次连接发固定 daily_minutes×1min TTL、
从不扣减已用,重连即崭新 10 分钟,日额度从未强制。改为账户级(全设备共享)
真卡控 + 累加式看广告加时:

- migration 000020: usage_daily 加 ad_bonus_minutes(sqlite+mysql)。
  当日额度 = plans.daily_minutes + ad_bonus_minutes;剩余 = 额度 − minutes_used。
- usage.store.AddAdBonusMinutes: 事务内累加封顶(替代布尔 MarkAdUnlocked),
  返回新总额+本次实际加时;GetDay/GetUsageRange 补读 ad_bonus_minutes。
- usage.service.UnlockAd: verify+nonce 后 +adBonusPerAd(10) 封顶 adDailyBonusCeiling(120),
  返回 granted+remaining;TodaySummary 加 MinutesCap/AdBonusMinutes。
- usage.ads DevVerifier: 放行式占位校验(nonce 防重放仍生效),接真 AdMob 前
  让看广告加时流程可端到端跑通;main.go 按 ADS_DEV_MODE/默认装配。
- ads/unlock: 204 → 200 返回 {granted_minutes, minutes_remaining}。
- ConnectNode 免费门: 读 AccountDayMinutes(used,bonus) → remaining≤0 拒 QUOTA_EXHAUSTED,
  否则 TTL=remaining(凭证到点硬切断兜底)。nodes.store 加 AccountDayMinutes。
- /me: 补 ad_bonus_minutes,quota_today_min 分母改 daily+bonus,加 quota_cap_min。
- quota.CheckFreeConnect 同步累加语义(免费基础 10 分钟不再需先看广告)。
- openapi + 契约/迁移版本/集成测试同步;新增 SQLite AddAdBonusMinutes 单测。

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

server/internal/store/sqlite_stores_test.go

@@ -58,6 +58,51 @@ func TestSQLite_UsageAccumulate(t *testing.T) {
 	}
 }
 
+// AddAdBonusMinutes 是免费版累加式看广告加时的核心原语:每次广告 +N 分钟,
+// 封顶 ceiling,返回新总额与本次实际加时(封顶后为 0)。
+func TestSQLite_AddAdBonusMinutes(t *testing.T) {
+	ctx := context.Background()
+	db := openSQLite(t)
+	us := usage.NewStore(db)
+	day := time.Date(2026, 6, 30, 0, 0, 0, 0, time.UTC)
+
+	// First ad on a fresh day → insert row, bonus 10.
+	newBonus, granted, err := us.AddAdBonusMinutes(ctx, 7, day, 10, 25)
+	if err != nil || newBonus != 10 || granted != 10 {
+		t.Fatalf("first: newBonus=%d granted=%d err=%v, want 10/10", newBonus, granted, err)
+	}
+
+	// Second ad → accumulate to 20.
+	newBonus, granted, err = us.AddAdBonusMinutes(ctx, 7, day, 10, 25)
+	if err != nil || newBonus != 20 || granted != 10 {
+		t.Fatalf("second: newBonus=%d granted=%d err=%v, want 20/10", newBonus, granted, err)
+	}
+
+	// Third ad → clamped at ceiling 25, so only +5 granted.
+	newBonus, granted, err = us.AddAdBonusMinutes(ctx, 7, day, 10, 25)
+	if err != nil || newBonus != 25 || granted != 5 {
+		t.Fatalf("third: newBonus=%d granted=%d err=%v, want 25/5", newBonus, granted, err)
+	}
+
+	// Fourth ad → already at ceiling, 0 granted.
+	newBonus, granted, err = us.AddAdBonusMinutes(ctx, 7, day, 10, 25)
+	if err != nil || newBonus != 25 || granted != 0 {
+		t.Fatalf("fourth: newBonus=%d granted=%d err=%v, want 25/0", newBonus, granted, err)
+	}
+
+	// Existing usage_daily columns are preserved alongside the bonus.
+	if err := us.AggregateUsage(ctx, 7, day, 0, 0, 4); err != nil {
+		t.Fatalf("aggregate: %v", err)
+	}
+	d, err := us.GetDay(ctx, 7, day)
+	if err != nil || d == nil {
+		t.Fatalf("getday: %v", err)
+	}
+	if d.AdBonusMinutes != 25 || d.MinutesUsed != 4 {
+		t.Errorf("getday wrong: bonus=%d used=%d, want 25/4", d.AdBonusMinutes, d.MinutesUsed)
+	}
+}
+
 // HasActiveSession 是「近实时远程下线」的服务端判据:有非吊销会话=在线,
 // 强制退出(RevokeByDevice)后=离线 → 客户端轮询到即登出。
 func TestSQLite_SessionHasActiveSession(t *testing.T) {