feat(go): add load simulator hold mode

docs/ops/100k-capacity-baseline.md

@@ -84,7 +84,8 @@ go run ./cmd/load-sim \
   -connect-rate 100 \
   -send-interval 10s \
   -duration 2m \
-  -template 0200
+  -template 0200 \
+  -send=false
 ```
 
 1. 100 连接 smoke test。

docs/ops/vehicle-ingest-runbook.md

@@ -104,7 +104,8 @@ go run ./cmd/load-sim \
   -connect-rate 100 \
   -send-interval 10s \
   -duration 2m \
-  -template 0200
+  -template 0200 \
+  -send=false
 ```
 
 ## 告警阈值建议

docs/superpowers/plans/2026-07-03-100k-vehicle-ingest-hardening.md

@@ -488,7 +488,7 @@ Extend load-sim to open N TCP connections and keep them open for `duration`, wit
 Expected CLI:
 
 ```bash
-go run ./cmd/load-sim -protocol jt808 -addr 115.29.187.205:808 -connections 10000 -send-interval 30s -duration 5m
+go run ./cmd/load-sim -protocol jt808 -addr 115.29.187.205:808 -connections 10000 -send-interval 30s -duration 5m -send=false
 ```
 
 - [ ] **Step 2: Run from non-production client**
@@ -496,7 +496,7 @@ go run ./cmd/load-sim -protocol jt808 -addr 115.29.187.205:808 -connections 1000
 Run a small smoke first:
 
 ```bash
-go run ./cmd/load-sim -protocol jt808 -addr 115.29.187.205:808 -connections 100 -duration 30s
+go run ./cmd/load-sim -protocol jt808 -addr 115.29.187.205:808 -connections 100 -duration 30s -send=false
 ```
 
 Then run 10K only after smoke succeeds.