[Umbrella] Drive large-scale production support for lakehouse integration

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/fluss/issues) and found nothing similar.

### Description

Fluss has initially achieved lakehouse-stream integration capabilities, but the following issues still need to be addressed in large-scale production environments.

### Willingness to contribute

- [ ] I'm willing to submit a PR!

This is an umbrella issue and names no files, tests, or entry points. Start by breaking the large-scale lakehouse production-support goal into concrete sub-issues and locating the existing lakehouse-stream integration work in the repository. Done requires specific production gaps to be identified, scoped, and addressed.

Written by the indexing model from the issue text.