feat: add gateway marketplace artifact API

[h1177h]

变更内容

本 PR 新增 gateway marketplace artifact 读取 API，用于通过 gateway 查询本地和云端 marketplace artifact。

主要包括：

• 新增 GET /market/artifacts
• 新增 GET /market/artifacts/{id}
• 新增 GET /market/artifacts/{id}/versions
• 接入本地 marketplace catalog
• 接入 cloud registry client，并叠加本地安装状态
• 补充 gateway marketplace artifact API 测试

不包含内容

本 PR 不包含 install、upgrade、uninstall、jobs、events、bindings 等写操作 API，后续单独提交。

测试

go test ./pkg/gateway ./pkg/marketplace ./pkg/marketplace/registry

[fennoai]

Found 3 issues worth addressing: two correctness regressions on the cloud read path, and one request-path performance/correctness problem in the local overlay step.

[codecov]

Codecov Report

❌ Patch coverage is 67.12963% with 71 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/gateway/gateway_market_artifacts_api.go	69.38%	49 Missing and 11 partials ⚠️
pkg/marketplace/registry/client.go	0.00%	5 Missing ⚠️
pkg/gateway/gateway_market_store.go	55.55%	2 Missing and 2 partials ⚠️
pkg/gateway/gateway_constructor.go	50.00%	1 Missing and 1 partial ⚠️

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