feat: search and inspect toolsets

[AlexTalreja]

Add toolsets page, which allows searching for specific toolsets and displaying respective tools.

[Yuan325]

What do you think about updating the term Search to Retrieve? Or List tools? Since user are not technically "searching" for the toolset but instead getting the list of tools within the toolset.

I realize that empty string toolset name does not work~ By default Toolbox will create a toolset with empty string "". So even if user did not specify a toolset in their config, they should have at least 1 toolset available (empty string).

After I retrieve a toolset -> click on a tool -> change the toolset name & click search -> the main content area still remain my previous tool's content. Can we update this to change main content back to the default "Welcome to MCP Toolbox UI" whenever user click the search button on 2nd nav bar?