chore(docker): 预装 Playwright MCP/CLI 及 chromium

镜像内全局预装 @playwright/mcp、@playwright/cli、playwright，并
`playwright install --with-deps chromium` 预置浏览器及系统依赖，运行时
不再联网下载。browser MCP 启动参数去掉 -y 与 @latest（改用已装好的本地版本）。

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

db/db.go

@@ -184,7 +184,7 @@ ON CONFLICT (agent_id, var_name) DO UPDATE
 INSERT INTO mcp_servers(name, transport, command, args, env, enabled)
 VALUES ('browser', 'stdio', 'npx', $1, '{}', false)
 ON CONFLICT (name) DO NOTHING`,
-		`["-y","@playwright/mcp@latest","--headless"]`); err != nil {
+		`["@playwright/mcp","--headless"]`); err != nil {
 		return fmt.Errorf("seed browser mcp: %w", err)
 	}
 	// NOTE: the placeholder ScopeSentry data-source MCP (empty URL + empty X-API-Key,