[FEATURE] Sort slash commands and @ references alphabetically

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Right now, when I write @ to reference a file or / to run a slash command, the drop down (in TUI) does not show the matches sorted alphabetically. This makes it inconvenient to find the exact match one is looking for.

Proposed Solution

Let us configure this behavior in settings.json:

1. Sort alphabetically (case sensitive)
2. Sort alphabetically (case insensitive)
3. Sort by recency
4. etc.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

1. I am writing a book
2. Its files are structured like this:

``
formats/typst/en_US/spiral-xx/part-yy/chap-zz/sec-aa.typ
``

1. @ Auto-completion shows these files in an unpredictable order:

formats/typst/en_US/spiral-01/part-01/_chap-03/sec-03.typ_
formats/typst/en_US/spiral-01/part-01/_chap-03/sec-01.typ_
formats/typst/en_US/spiral-01/part-01/_chap-03/sec-02.typ_
formats/typst/en_US/spiral-01/part-01/_chap-05/sec-03.typ_
formats/typst/en_US/spiral-01/part-01/_chap-05/sec-01.typ_
formats/typst/en_US/spiral-01/part-01/_chap-05/sec-02.typ_
formats/typst/en_US/spiral-01/part-01/_chap-01/sec-01.typ_
formats/typst/en_US/spiral-01/part-01/_chap-01/sec-02.typ_
formats/typst/en_US/spiral-01/part-01/_chap-04/sec-01.typ_
formats/typst/en_US/spiral-01/part-01/_chap-04/sec-02.typ_

The last two subdirs are displayed in haphazard order.

Additional Context

_No response_