Feat: robust Go edits in the codemods

### Which areas does this feature request relate to
- [x] Create Plugin

### Problem
The `experimental-app-sdk` codemod (#2856) is our first codemod that edits backend Go code, and it does it with regexes. That's brittle and likely to break across plugin variations.

### Solution
Find a more robust way to edit the Go source, ideally using AST but without requiring codemods to be written in Go.

### Alternatives

### Additional context

### Are you interested in contributing the solution?
- [ ] Yes
- [x] No

Start with the experimental-app-sdk codemod referenced in issue #2856 and inspect how its regexes edit backend Go code. Compare the approach across plugin variations and define a robust AST-based editing path that does not require codemods to be written in Go; done means the codemod reliably handles those variations.

Written by the indexing model from the issue text.