perf(queue): 按策略动态扩缩异步 Worker

将 River 执行容量按平台模型与用户组的有效并发策略动态调整，并为长任务续租、并发租约原子抢占和限流退避补充保护。\n\n统一平台模型限流继承语义，兼容历史 platformLimits/modelLimits，并为三个迁移图像模型建立独立并发租约。补充管理端显式继承/覆盖配置、指标、单元测试及隔离 PostgreSQL 验收。\n\n验证：go test ./... -count=1；pnpm lint；pnpm test；pnpm build；隔离 PostgreSQL 并发原子性/续租测试；128 任务与三分钟长任务动态 Worker 验收。

apps/api/internal/httpapi/model_catalog.go

@@ -487,18 +487,20 @@ func discountTitle(label string, discount float64) string {
 }
 
 func effectiveModelRateLimits(model store.PlatformModel, platform store.Platform, runtimePolicyMap map[string]store.RuntimePolicySet) ModelCatalogRateLimits {
-	overridePolicyRaw, hasOverridePolicy := model.RuntimePolicyOverride["rateLimitPolicy"]
-	overridePolicy := objectValue(overridePolicyRaw)
 	runtimePolicy := map[string]any(nil)
 	if model.RuntimePolicySetID != "" {
 		runtimePolicy = runtimePolicyMap[model.RuntimePolicySetID].RateLimitPolicy
 	}
-	policies := []rateLimitPolicySource{
-		{policy: overridePolicy, authoritative: hasOverridePolicy},
-		{policy: model.RateLimitPolicy, authoritative: len(model.RateLimitPolicy) > 0},
-		{policy: runtimePolicy, authoritative: strings.TrimSpace(model.RuntimePolicySetID) != ""},
-		{policy: platform.RateLimitPolicy},
-	}
+	policy := store.EffectiveRateLimitPolicy(store.EffectiveRateLimitPolicyInput{
+		BasePolicy:            model.BaseRateLimitPolicy,
+		PlatformPolicy:        platform.RateLimitPolicy,
+		RuntimePolicy:         runtimePolicy,
+		RuntimePolicyExplicit: model.RuntimePolicySetID != "",
+		RuntimePolicyOverride: model.RuntimePolicyOverride,
+		ModelPolicy:           model.RateLimitPolicy,
+		ModelPolicyMode:       model.RateLimitPolicyMode,
+	})
+	policies := []rateLimitPolicySource{{policy: policy, authoritative: policy != nil}}
 	limits := ModelCatalogRateLimits{
 		RPM:        firstRateLimit(policies, "rpm"),
 		TPM:        firstRateLimit(policies, "tpm_total"),