improvements to regex search/replace in the code editor

### Please check before submitting an issue

- [x] I am using the latest version of App Manager
- [x] I have searched the issues and haven't found anything relevant
- [x] I have read the docs
- [x] I know that generating a report, in whole part or in part, using AI/LLM is prohibited

### Describe the new feature

In the code editor, for search/replace, the current implementation regular expression implementation has some limitations.

Some things I noticed to be missing:
- Replace using capture groups
- Replace with an empty query (aka. remove all matching text)
- Match line starts with query "^" (which gives 0 matches currently)

It's what I found with some short-term use but there might be other things.

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start by locating the code editor's search/replace implementation and inspect how regular-expression matches are handled. Verify support for capture groups, empty replacements, and the ^ line-start pattern; done means each listed case works without producing zero or incorrect matches.

Written by the indexing model from the issue text.