fix(ui): right rail strip never scrolls: tabs shrink in proportion and clip their labels

A lane too short for the tab strip, even after the rail has climbed toward the HUD corner, shrank the strip into a scrollbar. The tabs now give way in proportion to their labels (flex 0 1 auto, min-height 0) and clip them at the end with a short fade; the join keeps corners no larger than half of a shrunken tab. The strip's scroll handling in placeJoin, the scroll listener, railJoinPath's tab-less path and the scroller marker are gone with the scrolling.

The expanded Radio Enable's reveal of the directory and Play lands its smooth scroll on scrollend when a rail layout pass, measuring the panels mid-scroll, puts the Context scroller's offset back and cancels it; the Radio browser gate stopped there since the strip-fit commit.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

docs/CURRENT-STATE.md

@@ -1487,7 +1487,9 @@ gives every owner-collapsed panel back. Stable Display allocation avoids
 unnecessary style writes.
 The compact Radio player is independent of Context: its launcher toggles it
 whether Context is collapsed or open, and only an outside pointer, Escape, its
-close button or its Details button closes it, never a layout pass.
+close button or its Details button closes it, never a layout pass. The
+expanded Enable's reveal of the directory and Play lands its smooth scroll
+even when a rail layout pass, measuring the panels, cuts it short.
 The right rail skips panels hidden by other CSS (computed `display: none`), but
 keeps the collapsed panels its own exclusive presentation hides, so the owner
 rule can still give them back.
@@ -1511,8 +1513,8 @@ the DOM so Tab from the open tab reaches the tool slot and then the panel.
 Labels are the panels' own translated header titles. The rail's lane shares
 the left rail's top; when it is too short for the strip, the rail climbs toward
 the HUD corner above as far as the strip needs (`src/ui/rightPanelRail.js`),
-and only a lane still shorter scrolls the strip, with a thin scrollbar and the
-open tab kept in view. Under the tabs the strip's
+and a lane still shorter shrinks the tabs in proportion, clipping their
+labels at the end; the strip never scrolls. Under the tabs the strip's
 column keeps a tool slot (`#right-rail-tools`) that holds the compact Radio
 launcher on desktop: `src/ui/radioPanelPlacement.js` moves it there from
 Context's header, and back for the phone sheet, so the compact player stays one