[Advanced Paste] Add a headless CLI for transformations

### Description of the new feature / enhancement

Add a supported, headless command-line interface for Advanced Paste transformations.

The CLI should accept clipboard content, stdin, or an input file and write the transformed result to stdout, the clipboard, or an output file. Initial coverage should prioritize deterministic, non-interactive transformations already supported by Advanced Paste, with a stable command structure, documented exit codes, and an optional machine-readable output mode.

Example shape:

```console
powertoys advanced-paste transform --format markdown --input notes.html
Get-Clipboard | powertoys advanced-paste transform --format plain-text
```

### Scenario when this would be used?

- Compose Advanced Paste transformations in PowerShell, batch files, build pipelines, and automation tools.
- Reuse PowerToys transformations without opening the Advanced Paste window or simulating keyboard input.
- Allow accessibility tools and agents to invoke a documented operation and consume predictable output.

### Supporting information

This should be a true headless interface rather than only a command that opens the existing UI. Commands should follow the repository's CLI conventions in `doc/devdocs/cli-conventions.md`.

Start by reading doc/devdocs/cli-conventions.md and reviewing how Advanced Paste transformations are currently exposed. The issue does not name an implementation entry point or tests. Done means a supported headless CLI accepts the stated input and output sources, documents exit codes, and provides the requested deterministic transformations and optional machine-readable output.

Written by the indexing model from the issue text.