feat: add marketplace registry server

[h1177h]

变更内容

本 PR 新增 marketplace registry server，用于提供 marketplace artifact 的发布、查询和管理能力。

主要包括：

• 新增 anyclaw-registry 命令入口
• 新增 marketplace registry HTTP server
• 新增 registry artifact、namespace、version 等数据结构
• 新增本地存储与 seed 初始化逻辑
• 补充 registry server 和命令入口测试

测试

go test ./cmd/anyclaw-registry ./pkg/marketregistry

[fennoai]

I found three noteworthy issues in the new registry server implementation. Tests pass locally, but they do not cover these trust-boundary and filesystem-safety cases.

[codecov]

Codecov Report

❌ Patch coverage is 63.54992% with 460 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/marketregistry/store.go	62.89%	133 Missing and 103 partials ⚠️
pkg/marketregistry/server.go	57.44%	124 Missing and 39 partials ⚠️
pkg/marketregistry/storage.go	64.28%	22 Missing and 18 partials ⚠️
cmd/anyclaw-registry/main.go	70.45%	11 Missing and 2 partials ⚠️
pkg/marketregistry/seed.go	90.80%	4 Missing and 4 partials ⚠️

📢 Thoughts on this report? Let us know!