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/runner/limits_test.go

@@ -102,8 +102,10 @@ func TestEffectiveRateLimitPolicyTreatsEmptyRuntimePolicyAsUnlimited(t *testing.
 		PlatformRateLimitPolicy: map[string]any{"rules": []any{
 			map[string]any{"metric": "rpm", "limit": 500},
 		}},
-		RuntimePolicySetID:     "runtime-policy-1",
-		RuntimeRateLimitPolicy: map[string]any{"rules": []any{}},
+		RuntimePolicySetID:       "runtime-policy-1",
+		RuntimePolicyExplicit:    true,
+		RuntimeRateLimitPolicy:   map[string]any{"rules": []any{}},
+		ModelRateLimitPolicyMode: "inherit",
 	})
 
 	if hasRules(policy) {