Deleted metadata components (destructive changes) are not surfaced in the Work Item Changes list

## Problem Description

When metadata components are deleted directly in a Salesforce org (e.g., Lightning
Pages / FlexiPages removed via Lightning App Builder or Setup), these deletions are
not surfaced in the DevOps Center Changes list and cannot be selected for inclusion
in a Work Item.

## Steps to Reproduce

1. Delete a Lightning Page (FlexiPage) from a dev sandbox via Setup or Lightning
App Builder
2. Open DevOps Center and navigate to the Work Item changes list
3. The deleted component does not appear — it cannot be selected or promoted

## Expected Behavior

Deleted components should appear in the Changes list, clearly marked as deletions
(destructive changes), so they can be included in a Work Item and promoted through
the pipeline like any other change.

## Actual Behavior

The deletion is invisible to DevOps Center. The only workaround is to manually
create a destructiveChanges.xml and deploy it via the Salesforce CLI, completely
bypassing DevOps Center. This breaks the single-pipeline principle and introduces
risk since the deletion is not tracked, reviewed, or validated through the normal
promotion flow.

## Impact

This forces teams to maintain two parallel deployment processes — one through
DevOps Center for additions/changes, and one through CLI for deletions. This
undermines the value of DevOps Center as a single source of truth for deployments
and increases the risk of inconsistencies between environments.

## Suggested Fix

Surface deleted components in the Changes list as destructive changes, similar to
how modified components are tracked. Allow them to be included in Work Items and
promoted through the pipeline with the same validation and review process.

## Environment

- DevOps Center version: NextGen
- Metadata type affected: FlexiPage (likely affects other metadata types as well)