perf(acceptance): 将 API 连接池提升至 64

P24 千并发在 API Pool 48 下仍出现 acquired 接近上限及 canceled acquire 增长，而 Worker Pool 仅使用 3 条连接，PostgreSQL 实际连接数仍有安全余量。

将生产 API Pool 默认值提升至 64，并允许通过 AI_GATEWAY_ACCEPTANCE_API_DATABASE_MAX_CONNS 配置单次验收；Worker 档位与 min-idle=4 保持不变。

验证：bash -n、ShellCheck、kubectl kustomize 和 git diff --check 通过。

scripts/cluster/run-production-acceptance.sh

@@ -51,9 +51,15 @@ require_commands curl git jq node openssl sed
 : "${AI_GATEWAY_ACCEPTANCE_USER_ID:?}"
 : "${AI_GATEWAY_ACCEPTANCE_GEMINI_MODEL:=}"
 : "${AI_GATEWAY_ACCEPTANCE_VIDEO_MODEL:=}"
+: "${AI_GATEWAY_ACCEPTANCE_API_DATABASE_MAX_CONNS:=64}"
 : "${AI_GATEWAY_ACCEPTANCE_GATEWAY_TLS_SERVER_NAME:=}"
 : "${AI_GATEWAY_ACCEPTANCE_GATEWAYS:?}"
 : "${AI_GATEWAY_ACCEPTANCE_REAL_IMAGE_URLS:?}"
+[[ $AI_GATEWAY_ACCEPTANCE_API_DATABASE_MAX_CONNS =~ ^[1-9][0-9]*$ &&
+   $AI_GATEWAY_ACCEPTANCE_API_DATABASE_MAX_CONNS -le 256 ]] || {
+  echo 'AI_GATEWAY_ACCEPTANCE_API_DATABASE_MAX_CONNS must be between 1 and 256' >&2
+  exit 1
+}
 
 node "$cluster_root/scripts/release-manifest.mjs" validate "$release_manifest" >/dev/null
 release_sha=$(node "$cluster_root/scripts/release-manifest.mjs" get "$release_manifest" sourceSha)
@@ -667,7 +673,7 @@ mark_run_failed() {
 apply_capacity_profile() {
   local profile=$1
   local slots pool media global
-  local api_pool=48
+  local api_pool=$AI_GATEWAY_ACCEPTANCE_API_DATABASE_MAX_CONNS
   local min_idle=4
   case $profile in
     P24) slots=24; pool=32; media=24; global=48 ;;
@@ -899,7 +905,7 @@ wait_for_memory_recovery() {
 
 verify_runtime_gates() {
   local expected_slots expected_global expected_pool
-  local expected_api_pool=48
+  local expected_api_pool=$AI_GATEWAY_ACCEPTANCE_API_DATABASE_MAX_CONNS
   case $active_profile in
     P24) expected_slots=24; expected_pool=32; expected_global=48 ;;
     P28) expected_slots=28; expected_pool=36; expected_global=56 ;;