fix: show '(co is thinking)' while reasoning streams instead of '(co thought)'

The reasoning toggle was appearing immediately when reasoning started,
showing '(co thought)' before the reasoning was complete. This was
confusing because 'co thought' implies past tense / completed action.

Changes:
- Show LiveStatusIndicator with 'thinking' status while reasoning streams
- Only show ReasoningToggle for completed messages from server
- Keep '(co is thinking)' visible throughout the reasoning phase
- Reasoning content only appears as expandable toggle after finalization

Now the UI correctly shows:
1. '(co is thinking)' - while reasoning is streaming
2. '(co is updating memory)' - when tool calls appear
3. '(co is saying)' - when assistant message streams
4. '(co thought)' - only on completed messages with reasoning