feat(design): titles in click surfaces stay selectable (E28 S3e4b)

A button whose text is a title or a name is now `selectable` (FocusSafeButton,
under Pressable and Button): Chrome selects inside a button once it is
user-select: text (measured), and the click that ends a selection, or a press
dragged past the slop, opens nothing. 23 surfaces carry it (cards, rows, people,
channels, playlists, users, views, messages, log lines, description links); the
Plex caption div gets the same guard. A contract test pins every plain Pressable
with its reason, so a new one has to choose.

frontend/src/components/plexDetailUi.tsx

@@ -59,6 +59,7 @@ export function Filterable({
   if (!onClick) return <span className={className}>{children}</span>;
   return (
     <Pressable
+      selectable
       onClick={onClick}
       title={hint}
       // min-h-6 + touch-target: a value in the meta line is still a 24 / 44 target (B1, A3).