fix(frame): start the corner fade at the brightest palette stop

A ladder is a hue walk, not a brightness walk, so painting the hot end
backwards put the dim colour at the corner.  Sort the ramp by stock
brightness and follow the pane height for the bottom-left glow.

beefy_player/widgets/frame.py

@@ -2,8 +2,9 @@
 
 The panes draw their own frames instead of using Textual's ``border`` so the
 corners can be coloured.  Two of them — the top right and the bottom left —
-run a short fade out of the palette's hot end and back into the border grey;
-everything else, including the other two corners, is that grey.
+run a short fade out of the palette's hot end and back into the border grey,
+brightest colour at the corner; everything else, including the other two
+corners, is that grey.
 
 The ladder is whatever palette the app is on (``c`` cycles them), which is why
 every function here takes ``stops`` rather than reading a module constant.
@@ -11,12 +12,14 @@ every function here takes ``stops`` rather than reading a module constant.
 
 from __future__ import annotations
 
+from functools import cache
+
 from rich.cells import cell_len
 from rich.console import Group, RenderableType
 from rich.text import Text
 from textual.widget import Widget
 
-from ..palettes import DEFAULT_PALETTE, PALETTES
+from ..palettes import DEFAULT_PALETTE, PALETTES, brightness
 from .common import active_stops
 
 #: The frame itself: one grey, the same grey as the scrollbar thumb.
@@ -26,20 +29,32 @@ EDGE = "bright_black"
 FADE_CELLS = 4
 
 
+@cache
+def fade_ramp(stops: tuple[str, ...]) -> tuple[str, ...]:
+    """The corner ramp: brightest cell first, border grey past its end.
+
+    The colours come from the palette's hot end, but a ladder is a hue walk,
+    not a brightness walk: ``spectrum`` ends on ``red``, which is dimmer than
+    the ``yellow`` just before it, so painting the ladder backwards put the
+    dim colour at the corner and the glow out on the edge.  Sorting the hot
+    end by brightness keeps the corner the brightest cell and dims outwards,
+    whatever theme sits behind the names.
+    """
+    hot = [name for name in stops if name != EDGE][-FADE_CELLS:]
+    return tuple(sorted(hot, key=brightness, reverse=True))
+
+
 def corner_fade(distance: int, stops: tuple[str, ...] = ()) -> str:
     """Colour ``distance`` cells out from a corner; 0 is the corner glyph.
 
-    The fade is short — four cells — and walks backwards down the palette from
-    its hot end, so the corner glows in the palette's brightest colour and then
-    hands over to the plain border grey.
+    The fade is short — four cells — and runs from the brightest colour the
+    palette's hot end offers back into the plain border grey.
     """
     if not stops:
         stops = PALETTES[DEFAULT_PALETTE]
+    ramp = fade_ramp(tuple(stops))
     distance = max(0, distance)
-    if distance >= FADE_CELLS:
-        return EDGE
-    index = len(stops) - 1 - distance
-    return stops[index] if index >= 0 else EDGE
+    return ramp[distance] if distance < len(ramp) else EDGE
 
 
 def inner_size(width: int, height: int) -> tuple[int, int]:
@@ -119,7 +134,6 @@ def wrap(
     width = max(4, width)
     height = max(2, height)
     inner_width, inner_height = inner_size(width, height)
-    rows = len(lines[:inner_height])
 
     framed: list[Text] = [top(width, title, stops)]
     for index, line in enumerate(lines[:inner_height]):
@@ -129,12 +143,12 @@ def wrap(
             line = line.copy()
             line.truncate(inner_width, overflow="ellipsis")
         row = Text(no_wrap=True)
-        row.append_text(side_row(index, rows, "left", stops))
+        row.append_text(side_row(index, inner_height, "left", stops))
         row.append_text(line)
         pad = inner_width - cell_len(line.plain)
         if pad > 0:
             row.append(" " * pad)
-        row.append_text(side_row(index, rows, "right", stops))
+        row.append_text(side_row(index, inner_height, "right", stops))
         framed.append(row)
     while len(framed) < height - 1:
         index = len(framed) - 1