* refactor(ui): share one panel tab strip between terminal and browser
Extract the terminal tab strip (tab + attached close button as one
surface, from #108611) into a shared panel-tab-strip module and migrate
the in-app browser panel onto it. The browser tabs inherit the attached
close design; terminal tabs gain middle-click close and long-label
ellipsis; both get the empty-group workaround and a strip that shrinks
inside the flex header. Net -24 prod LOC; duplicated tp-/bp- strip CSS
deleted.
* fix(ui): keep shared panel new-tab button stable