Fix #1468: Arrow keys and backspace in the server console

[iManGaaX]

Summary

Console input used a single counter for both the text length and the cursor position, so pressing Left and then Backspace deleted the wrong character and blocked Right afterwards; the input line now keeps a real cursor position: characters are inserted/removed at the cursor, and Left/Right, Backspace and Delete all work as expected; when stdin/stdout are redirected nothing changes

Closes #1468.

Before ->

2026-09-13.04-34-27.mp4

After ->

2026-09-13.04-43-08.mp4

Checklist

• Your code should follow the coding guidelines.
• Smaller pull requests are easier to review. If your pull request is beefy, your pull request should be reviewable commit-by-commit.

[Fernando-A-Rocha]

You should put this in #5288 😅

[iManGaaX]

You should put this in #5288 😅

In the current PR, i fixed a bug for an existing feature, but the PR u r talking about is an enhancement, which is hard to get merged right now due to the feature freeze