fix(playback): keep the play button glyph above 3:1 on 1x displays

Electron E2E on Windows measured the hovered play icon at 2.5:1 against
its fill (`player-theme.e2e.ts`, white-backing rasterization). White on
the #4f8eff accent is only 3.2:1 in theory, and the hover scale(1.04)
resampled the glyph, so a 1x display's antialiasing pushed it under 3:1.

- Fills under a white glyph (play, active tune) use a deeper
  --pc-accent-blue-strong #3474e8 (4.4:1); hover darkens to #2a66d6
  (5.3:1). The track fill and glow keep the #4f8eff accent.
- The play button no longer scales on hover.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture/player-controls-contract.md

@@ -335,9 +335,12 @@ app's `--app-selection-color` is a different blue that would fight the video.
   recording, picture-in-picture and fullscreen, end-aligned.
 - **Play button** (`.player-controls__play`, `data-test-id
   ="player-controls-play"`): a 52px filled accent circle with a white glyph,
-  not a Material icon button. Hover darkens the fill rather than lightening
-  it so the glyph keeps ≥3:1 against it — `player-theme.e2e.ts` rasterizes
-  exactly the hovered and focused states.
+  not a Material icon button. Fills under a white glyph (play, active
+  `tune`) use `--pc-accent-blue-strong` `#3474e8` (4.4:1) rather than the
+  `#4f8eff` accent (3.2:1), and hover darkens to `#2a66d6` (5.3:1) without
+  scaling — `player-theme.e2e.ts` rasterizes the hovered and focused
+  states, and on a 1x Windows display the antialiased or resampled glyph
+  measured below 3:1 against the lighter fills.
 - **Icon buttons** are 40px with a 12px radius (32px / 9px compact) through
   Material's `--mat-icon-button-*` tokens; their hover is a flat
   `rgba(255,255,255,.1)` layer.

libs/ui/playback/src/lib/player-controls/player-controls.component.scss

@@ -5,7 +5,11 @@
     // tokens of the "Hybrid" controls concept (accent blue = primary action
     // and progress; cyan = something is on; violet = a value was changed).
     --pc-accent-blue: #4f8eff;
-    --pc-accent-blue-hover: #3f7ef5;
+    // Fills that carry a white glyph (play, active tune) use deeper blues:
+    // white on #4f8eff is only 3.2:1, too close to the 3:1 floor once a
+    // 1x display antialiases the glyph. These give 4.4:1 and 5.3:1.
+    --pc-accent-blue-strong: #3474e8;
+    --pc-accent-blue-hover: #2a66d6;
     --pc-accent-cyan: #5cd6ff;
     --pc-accent-violet: #b599ff;
     --pc-text: #e7ecf3;
@@ -389,7 +393,7 @@
 :host :is(.player-controls__tune--active),
 :host :is(.player-controls__tune--active:hover) {
     color: #ffffff;
-    background: var(--pc-accent-blue);
+    background: var(--pc-accent-blue-strong);
     --mat-icon-button-icon-color: #ffffff;
 }
 
@@ -431,14 +435,12 @@
     border: 0;
     border-radius: 50%;
     color: #ffffff;
-    background: var(--pc-accent-blue);
+    background: var(--pc-accent-blue-strong);
     box-shadow:
         0 0 0 6px rgba(79, 142, 255, 0.18),
         0 6px 20px rgba(79, 142, 255, 0.35);
     cursor: pointer;
-    transition:
-        background 120ms ease-out,
-        transform 120ms ease-out;
+    transition: background 120ms ease-out;
 }
 
 .player-controls__play mat-icon {
@@ -448,11 +450,11 @@
     color: #ffffff;
 }
 
-// Hover darkens rather than lightens: the white glyph keeps its contrast
-// against the fill (the theme E2E rasterizes exactly this state).
+// Hover darkens rather than lightens, and does not scale: the white glyph
+// keeps its contrast against the fill, and a scaled glyph is resampled and
+// blurred on 1x displays (the theme E2E rasterizes exactly this state).
 .player-controls__play:hover:not(:disabled) {
     background: var(--pc-accent-blue-hover);
-    transform: scale(1.04);
 }
 
 .player-controls__play:focus-visible {