Auto-delete closing tag when opening tag becomes self-closed

まだ誰も着手していません。

When I type a paired tag, for example:

```tsx

```

If I then add a slash at the end of the opening tag to make it self-closing:

```tsx

```

The editor leaves the redundant closing tag untouched, resulting in broken/invalid markup.

https://github.com/user-attachments/assets/b4335989-09ba-423c-a79e-3f6a69c0275f

**Expected behavior:**

```tsx

```

https://github.com/user-attachments/assets/b9a5a910-5927-48ff-bbbd-0036d96e03c1

Reproduce the issue with the TSX example in the report by adding a slash to the opening tag, then trace the editor behavior responsible for paired-tag handling. Done means converting to without leaving the redundant closing tag; add or run a regression test if the relevant test location is found.

索引モデルが issue の本文から書いたものです。