Feature request: directive option to suppress the subcommands group heading without hiding subcommands

Hello,

I'm a contributor of https://github.com/qgis-deployment/qgis-deployment-toolbelt-cli (aka QDT) and https://github.com/opengisch/qgis-plugin-ci/ where we are successfully using your project. Thanks for that, it's really useful and well designed.

We're facing an issue with sub-commands display with a duplicate header:

When documenting a CLI that has subcommands, a common pattern is to document the root parser once (to show global options) and then document each subcommand individually via :path:. When the root parser uses add_subparsers(title="..."), sphinx-argparse renders that title as an h2 heading inside the root parser block even though the subcommands are already documented below it. This creates a duplicate or orphan heading with no useful content.

Steps to reproduce

Given a parser like):

subparsers = main_parser.add_subparsers(title="Sub-commands", dest="command")

And a documentation file using:

```{argparse}
  :module: my_wonderful_pypkg.cli
  :func: build_parser
  :prog: wonderful
  :noepilog:
```

The first directive renders a Sub-commands h2 heading listing the subcommands. The subcommands are then documented individually below. Result: a duplicate heading in the page structure.

Workarounds and drawbacks

• :nosubcommands:: suppresses the subcommands list entirely, but also removes the heading. This is too coarse since the list is useful, only the heading is unwanted.

• removing title= from add_subparsers() in the source code fixes the rendering, but alters the --help output of the CLI itself which is not what we want.

• using :path: directives manually in the rst/md file but it requires more. It's what we're doing for now. And there is antoher issue: help is not displayed.

  • this block:

  ```{argparse}
    :module: qgis_deployment_toolbelt.cli
    :func: build_parser
    :path: deploy
    :prog: qdt
  ```
  

  • renders (note that the subcommand help is not displayed as description, in contrary with the first screenshot):
  

Proposed solution

Add a new directive option, for example :nosubcommandstitle: (or a more generic :nogroupheading:), that suppresses the heading generated for the subparser action group while keeping the list of subcommands intact.

Alternatively, a :nogrouptitles: option could suppress headings for all argument groups whose content would otherwise be empty or redundant, giving more control without requiring per-group options.

Environment

• sphinx-argparse 0.5.2
• Sphinx 9.1.0
• MyST-Parser (directive used as {argparse} in Markdown)

Start at the {argparse} directive handling for :nosubcommands: and the rendering of the add_subparsers(title="Sub-commands") action group. Add a directive option that suppresses only the group heading while retaining the subcommand list, then verify it with the reproduction configuration and confirm that :nosubcommands: behavior remains unchanged.