## Summary
This PR updates Go agent publish logic to persist the parent canvas
update and canvas-version save in the same transaction.
## Changes:
- Reuse SaveOrReplaceLatest semantics for published versions
- Add SaveOrReplaceLatestTx for transactional publish flow
- Keep canvas release update and version persistence atomic
- Add a focused publish test covering canvas and released version state
## Tested:
```
bash build.sh --test -run 'Test(PublishAgentUpdatesCanvasAndReleasedVersion|UpdateAgentDSLCreatesAndReplacesDraftVersion|
UpdateAgentDSLDoesNotOverwriteLatestReleasedVersion)$' ./internal/service ./internal/dao
```
<img width="1476" height="850" alt="image"
src="https://github.com/user-attachments/assets/2c576581-1143-420b-8750-a77aa3c4292d"
/>
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