Pending reviews created through the API went through `SubmitReview`,
which added a timeline entry and sent notifications before the review
was submitted, so submitting it later showed the review twice.
- Pending reviews skip the timeline entry and notifications until
submitted, like on GitHub
- `CreatePullReview` rejects comments without a `path` or a positive
line with 422, like GitHub
- Already duplicated reviews stay as they are
Fixes https://github.com/go-gitea/gitea/issues/40259
Assisted-by: Claude Code:claude-opus-5-5
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Co-authored-by: silverwind <me@silverwind.io>
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