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/PlaylistsRail.tsx

@@ -329,6 +329,7 @@ export default function PlaylistsRail({
                 // A sibling of the row button, not inside it — a button cannot hold a button.
                 <div key={pl.id} className="group relative" {...railMenu.triggerProps(pl)}>
                   <Pressable
+                    selectable
                     ref={(el) => {
                       if (pl.id === selectedId) selectedRef.current = el;
                       // Back from the rename field by Enter/Escape — see refocusRowRef.