refactor(ui): move tool details icon to header row
Moved the tool details info icon from bottom-right of the message to the
header row, positioned to the left of the chevron. This is cleaner and
more intuitive.
Layout is now:
(co recalled) ⓘ ∨
Changes:
- MessageGroupBubble: Added tool details button in header with state
- ToolCallItem: Accepts showToolDetails prop from parent (no local state)
- Removed bottom-right positioning, now controlled by header button