Show warning message when last user input get pruned

[Jazzcort]

Description

If the user's last input is pruned due to context overflow, a warning message will be displayed in the chat section, alerting them that some details may have been lost. As a result, the response they receive might be incomplete or inaccurate due to the truncated input. https://github.com/Granite-Code/granite-code/issues/22

Screenshots

Testing instructions

Set the model’s context length to a small value (e.g., 512) and ask a question that exceeds contextLength - maxTokens tokenwise. A warning message will appear at the bottom of the chat section, indicating that some input may have been truncated. Deleting previous messages will remove the warning.