feat(secrets-mcp): /changelog 页（Markdown 渲染）、首页与 Dashboard 入口

- 新增 CHANGELOG.md 构建嵌入、pulldown-cmark 渲染、路由 /changelog
- 首页页脚与 MCP Dashboard 页脚提供变更记录链接；同步 README、AGENTS
- 版本 secrets-mcp 0.5.24

crates/secrets-mcp/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "secrets-mcp"
-version = "0.5.21"
+version = "0.5.24"
 edition.workspace = true
 
 [[bin]]
@@ -45,3 +45,4 @@ urlencoding = "2"
 schemars = "1"
 http = "1"
 url = "2"
+pulldown-cmark = "0.13.3"