Revisit target framework defaults and selection in `aspire new` for .NET 11

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

.NET 11 is currently an opt-in target framework in the Aspire project templates, while `net10.0` remains the default. The underlying `dotnet new` templates allow users to opt in explicitly, for example:

```console
dotnet new aspire-starter --framework net11.0
```

However, `aspire new` does not expose or forward the template's `Framework` option. Consequently, users of the Aspire CLI cannot select a supported target framework and must either use `dotnet new` directly or edit all generated project files afterward.

This gap has surfaced previously:

- #9931 explicitly reported that `aspire new` lacked framework selection, but was closed after `net10.0` became the default.
- #19050 revisited the default when only .NET 11 was installed and was closed as by design because preview TFMs are opt-in. A follow-up comment highlighted that `aspire new` provides no way to perform that opt-in.
- #9480 added per-template option handling to `aspire new`, but the target-framework option is not currently among the options exposed for the C# templates.

### Describe the solution you'd like

Revisit target-framework behavior in `aspire new` as part of .NET 11 support and make explicit decisions for both of these questions:

1. **Default:** When should the C# Aspire templates change their default target framework from `net10.0` to `net11.0`?
2. **Selection:** Should `aspire new` expose `-f|--framework ` for templates containing .NET projects, matching the supported values defined by the underlying template?

If framework selection is added, expected behavior would include:

```console
aspire new aspire-starter --framework net11.0
aspire new aspire-empty --framework net10.0
```

- The option is shown in template-specific help with the supported values.
- The selected framework is applied consistently to every generated .NET project.
- Non-interactive usage can select a framework without prompts.
- Omitting the option continues to use the template's documented default.
- Templates that do not contain .NET projects do not expose the option.

### Additional context

SDK selection, Aspire template/package version selection, and project target-framework selection are separate concerns. The existing `aspire new --version` option selects the Aspire project-template package version; it does not select the generated projects' target framework.

Related framework-support history: #18849 added opt-in .NET 11 support, while #12267 changed the template default to .NET 10 shortly before .NET 10 GA.

Start at the `aspire new` CLI entry point and review the per-template option handling added in #9480, then compare it with the C# templates' supported `Framework` option. Define the default and selection behavior, including help, non-interactive use, consistent application to generated projects, and omission for templates without .NET projects.

Written by the indexing model from the issue text.