merge: maestro/tsk_x7wrlA87orsY [devices + 订阅校验中间件] (tsk_VRzw-af__qWx)

手动合并 tsk_x7wrlA87orsY（设备管理 + 订阅校验中间件）到 main：

冲突解决：
- server/internal/apierr/apierr.go：保留 tsk_GXDoc3Cs07Rn 版本（New/StatusFor/
  Middleware/ErrConflict/改善文档），并入 tsk_x7wrlA87orsY 新增的 ErrAccountBanned
  及对应 StatusFor case（→ 403）。

新增文件（来自 tsk_x7wrlA87orsY）：
- server/internal/devices/doc.go       package 文档（替换占位 stub）
- server/internal/devices/context.go   CtxKeyUserID / Plan / WithPlan / PlanFromCtx
- server/internal/devices/handler.go   GET /v1/me/devices · DELETE /v1/me/devices/{id}
- server/internal/devices/middleware.go SubscriptionMiddleware · CheckDeviceQuota · RequirePaidTier
- server/internal/devices/service.go   RegisterIfAbsent / DeleteDevice / ResolvePlan + 纯函数 resolveEffectivePlan
- server/internal/devices/store.go     MySQL 数据访问层
- server/internal/devices/service_test.go          15 个单测（全通过）
- server/internal/devices/devices_integration_test.go  testcontainers 集成测试

OpenAPI 更新（来自 tsk_x7wrlA87orsY）：
- server/api/openapi.yaml：SubscriptionInfo.source 枚举补 free
- design/server/openapi.yaml：SubscriptionInfo.source 枚举补 admin, free

测试：go build ./... ✓；go test ./internal/apierr/... ✓（8 tests）；
      go test ./internal/devices/... ✓（15 tests）。

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/internal/devices/context.go

@@ -0,0 +1,80 @@
+package devices
+
+import (
+	"context"
+	"time"
+)
+
+// ctxKey is a private type for context keys to avoid collisions.
+type ctxKey string
+
+// CtxKeyUserID is the context key under which the authenticated user's
+// internal int64 ID is stored by the JWT auth middleware (module #2).
+//
+// It mirrors the key used by the codes module so that, once the auth
+// middleware lands, a single canonical key can be reconciled across modules.
+const CtxKeyUserID ctxKey = "user_id"
+
+// ctxKeyPlan is the context key under which the resolved subscription Plan is
+// stored by SubscriptionMiddleware.
+const ctxKeyPlan ctxKey = "plan"
+
+// WithUserID returns a copy of ctx carrying the authenticated user ID.
+// Primarily used in tests and by the auth middleware.
+func WithUserID(ctx context.Context, userID int64) context.Context {
+	return context.WithValue(ctx, CtxKeyUserID, userID)
+}
+
+// UserIDFromContext extracts the authenticated user ID from ctx.
+// ok is false when no (valid) user ID is present.
+func UserIDFromContext(ctx context.Context) (int64, bool) {
+	v, ok := ctx.Value(CtxKeyUserID).(int64)
+	if !ok || v == 0 {
+		return 0, false
+	}
+	return v, true
+}
+
+// Plan is the resolved effective subscription for a user, injected into the
+// request context by SubscriptionMiddleware and consumed by nodes (catalogue
+// filtering, connect), usage (daily caps), and the /v1/me summary.
+type Plan struct {
+	// PlanCode is one of "free", "pro", "team".
+	PlanCode string
+	// ExpiresAt is the effective subscription expiry (UTC); nil for the free
+	// fallback when the user has no active paid/trial subscription.
+	ExpiresAt *time.Time
+	// MaxDevices is the per-plan device cap (free 1 / pro 5 / team 10).
+	MaxDevices int
+	// DailyMinutes is the free-plan daily time cap in minutes; nil = unlimited.
+	DailyMinutes *int
+	// AdGate is true when the user must watch a rewarded ad to unlock daily use.
+	AdGate bool
+	// Source is the subscription source: "trial", "code", "admin", or "free"
+	// for the no-subscription fallback.
+	Source string
+}
+
+// WithPlan returns a copy of ctx carrying the resolved Plan.
+func WithPlan(ctx context.Context, p Plan) context.Context {
+	return context.WithValue(ctx, ctxKeyPlan, p)
+}
+
+// PlanFromCtx extracts the resolved Plan from ctx. ok is false when
+// SubscriptionMiddleware has not run.
+func PlanFromCtx(ctx context.Context) (Plan, bool) {
+	p, ok := ctx.Value(ctxKeyPlan).(Plan)
+	return p, ok
+}
+
+// planTier maps a plan code to a numeric tier (higher = better) for comparison.
+func planTier(code string) int {
+	switch code {
+	case "team":
+		return 3
+	case "pro":
+		return 2
+	default: // "free" or unknown
+		return 1
+	}
+}