[FEATURE] Ensure Java / Kotlin code is marked as generated

### Why do we need this improvement?

This improvement is needed so that generated code can easily be excluded from quality analysis by standard JVM tooling.

### How will this change help?

Some quality tools allow exclusion by filesystem path or package; others require annotations to exclude the code. This change will improve ease of use for JVM-based consumers.

### Screenshots

_No response_

### How could it be implemented/designed?

Any generated class must be annotated with `jakarta.annotation.Generated` to simplify excluding the code from various quality tools.

### 🚧 Breaking changes

No

### 👀 Have you checked for similar open issues?

- [x] I checked and didn't find a similar issue

### 🏢 Have you read the Contributing Guidelines?

- [x] I have read the [Contributing Guidelines](https://github.com/asyncapi/.github/blob/master/CONTRIBUTING.md)

### Are you willing to work on this issue?

No, someone else can work on it.

No files or tests are named in the issue. Start by locating the generator entry points and Java/Kotlin templates, then determine where generated classes are produced. Done means every generated class carries the requested jakarta.annotation.Generated annotation and the relevant generation checks pass.

Written by the indexing model from the issue text.