feat(acceptance): 建立同构验收与弹性容量体系

实现本地三节点 K3s 同构环境、脱敏生产快照、Gemini 图片和多参考图视频协议模拟、统一验收报告及故障注入。\n\n新增 Worker 容量控制器、资源与连接预算、任务恢复保护，并将生产验收拆分为 validation 执行和人工 CAS 放量。\n\n验证包括 Go 全量测试、PostgreSQL HTTP 集成测试、go vet、OpenAPI、ShellCheck、前端检查、迁移及发布脚本测试。

scripts/acceptance/export-production-snapshot.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+usage() {
+  cat <<'EOF'
+Usage:
+  AI_GATEWAY_ACCEPTANCE_SNAPSHOT_DATABASE_URL='postgresql://...' \
+    scripts/acceptance/export-production-snapshot.sh \
+      --release-sha <full-sha> --output <snapshot.json>
+
+This command is database read-only. The supplied role should have SELECT access
+only. It never prints the database URL or candidate credentials.
+EOF
+}
+
+script_dir=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+repository_root=$(cd "$script_dir/../.." && pwd)
+
+[[ ${1:-} == --release-sha && ${3:-} == --output && $# -eq 4 ]] || {
+  usage >&2
+  exit 64
+}
+release_sha=$2
+output=$4
+database_url=${AI_GATEWAY_ACCEPTANCE_SNAPSHOT_DATABASE_URL:-}
+
+[[ $release_sha =~ ^[0-9a-f]{40}$ ]] || {
+  echo 'release SHA must be a full lowercase Git SHA' >&2
+  exit 64
+}
+[[ -n $database_url ]] || {
+  echo 'AI_GATEWAY_ACCEPTANCE_SNAPSHOT_DATABASE_URL is required' >&2
+  exit 64
+}
+umask 077
+(
+  cd "$repository_root/apps/api"
+  AI_GATEWAY_DATABASE_URL="$database_url" \
+    go run ./cmd/acceptance-snapshot export \
+      --release-sha "$release_sha" \
+      --output "$output"
+)
+chmod 0600 "$output"