fix(ai): handle unknown finish_reason in openai-completions gracefully

Map unknown finish_reason values (e.g. "end" from Ollama/LM Studio) to
"stop" instead of throwing, since assistant content is already produced.

fixes #2142

packages/ai/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Handle `finish_reason: "end"` from Ollama/LM Studio by mapping it to `"stop"` instead of throwing ([#2142](https://github.com/badlogic/pi-mono/issues/2142))
+
 ## [0.58.0] - 2026-03-14
 
 ### Added