Web Chat Settings left the System Prompt field empty but still treated a
blank/whitespace value as an explicit system turn. That satisfied
tokenizer chat templates' messages[0].role == system check and suppressed
the model YAML system_prompt on fresh chats.
Omit empty/whitespace system messages in the React and Alpine UIs, strip
them server-side, and inject config.SystemPrompt for tokenizer-template
models when the request has no real system turn.
Fixes#11834
Signed-off-by: lei_lei <96427312+leilei3167@users.noreply.github.com>
lei_lei
7c921aa020