The tool-card border-subtle was so faint that the cards visually melted
into the surrounding prose once the cursor left the conversation. Bumps
the resting border to --border-muted and adds a 2px left edge so a tool
output row reads as metadata at a glance, even on light skins where
border-subtle is barely visible. Hover still escalates to --border2.
Verified by loading a session with mixed tool calls and assistant prose
on the light theme and confirming the tool cards are now identifiable
without mousing over them.
Refs #2867
Sanjay Santhanam
d86e841f0b
