Fit comment marker touch areas to the first line and return Back to its item

On a coarse pointer the marker's hit area keeps 44px of width but is no
taller than the block's first line, so a tap at the end of the second
line reaches the text. A slim chip with ten or more threads widens to
18px so two digits never clip. Back from a thread to its block's list
focuses the item it came from, on desktop and in the compact sheet.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>