Allow using $path and $mcp placeholders in the string-type href option in the Contextual Menu

[novusnota]

The contextual menu can be extended with custom options given in the "contextual" → "options" field of the docs.json.

Each custom option requires a href field, either as a string or as an object. The problem here is that the special placeholders, such as $path, $page, and $mcp, are only allowed when href is given as an object, but not allowed when it is a string.

Please, allow using at least the $path placeholder in the string-type href option, such that resulting URLs can be given as follows:

{
  // ...
  "href": "https://example.com/?page=$page"
  // ...
}

Here's a real-world example of a docs.json snippet that could happen if you port such small feature from hrefs objects to hrefs links:

{
  // ...
  "contextual": {
    "options": [
      {
        "title": "Open in GitHub",
        "description": "Open this page in the GitHub repository",
        "href": "https://github.com/ton-org/docs/blob/main/$page",
        "icon": "github"
      },
      "copy",
      "chatgpt",
      "claude",
      "perplexity",
      "mcp",
      "cursor",
      "vscode"
    ]
  },
  // ...
}