CmdPal: Run should support autocompleting env vars

### Description of the new feature / enhancement

I have two features that I used a lot in PowerToys Run that don't work the same in CmdPal:

1. Show environment variables in file search results
2. Ability to enter tool shortcut after you've started typing

### Scenario when this would be used?

# Show environment variables in file search results:

## PowerToys Run Behaviour:

1. Attempting to open `%userprofile%`
2. Type `%user` in CmdPal
3. `%userprofile%` is the top result, press enter to open the folder

## CmdPal Behaviour:

Currently, you have to type out the entire `%userprofile%` in order for this to display in CmdPal, and even then it's the second option.

Second request that was a dupe of #38877

# Ability to enter tool shortcut after you've started typing

## PowerToys Run Behaviour:

1. Type `display` in the search box
2. Realise you only wanted to search in settings
3. Navigate back to the start of the line and type `$`
4. Only results from settings are displayed

## CmdPal Behaviour:
After adding the `$` at the start of the search query, only web and file fallback results are displayed

Start with CmdPal's search behavior and the file-search results described in the issue. Reproduce typing `%user` and adding `$` after an existing query, then trace the relevant autocomplete and shortcut handling; done means environment variables appear as top results and shortcut-scoped results remain available in both cases.

Written by the indexing model from the issue text.