fix(0.3.1): My Radio layout polish + drop dark-auto

Real-screen review of v0.3.0 surfaced a contrast bug and several layout
issues. Quick patch.

- Drop @media prefers-color-scheme dark for theme=auto. WP admin has
  no native dark mode, so OS-dark made our light text sit on the still-
  white WP postbox = unreadable. `auto` now behaves as light; `dark`
  remains as an explicit choice.
- theme=dark now actually reads: the player surface itself goes dark
  (#1d2327 bg + subtle border + padding) so the light text has somewhere
  to land instead of fighting the white WP postbox.
- .radio-wrap max-width 880px — player no longer stretches edge-to-edge.
- Drop the .radio-intro max-width:720px cap so the intro fits one line.
- Volume slider fixed at flex:0 0 auto / width:220px — % label sits next
  to the slider instead of pinned to the far edge.
- Station dropdown capped at 360px (was width:100%).
- Play-button dashicon shrunk 18px → 14px so it sits on the button-text
  baseline instead of looking like a second row.

Files: radio.php, assets/css/radio.css, inc/about.php, CHANGELOG.md.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

assets/css/radio.css

@@ -87,9 +87,9 @@
 }
 
 .radio-player__play .dashicons {
-    font-size: 18px;
-    width: 18px;
-    height: 18px;
+    font-size: 14px;
+    width: 14px;
+    height: 14px;
     line-height: 1;
 }
 
@@ -97,8 +97,8 @@
     display: flex;
     align-items: center;
     gap: 8px;
-    flex: 1;
-    min-width: 200px;
+    flex: 0 0 auto;
+    width: 220px;
 }
 
 .radio-player__volume .dashicons {
@@ -160,7 +160,7 @@
 
 .radio-player__station-select select {
     width: 100%;
-    max-width: 100%;
+    max-width: 360px;
 }
 
 /* Error notice — uses WP notice styling */
@@ -195,9 +195,15 @@
 }
 
 /* ──────────────────────────────────────────────────────────────────
- * Main admin page — wrap player in a postbox-like card
+ * Main admin page — wrap player in a postbox-like card.
+ * Constrained max-width keeps the player a focused settings-page card
+ * instead of stretching to fill the full admin width.
  * ─────────────────────────────────────────────────────────────── */
 
+.radio-wrap {
+    max-width: 880px;
+}
+
 .radio-wrap .radio-player {
     margin-top: 4px;
 }
@@ -206,7 +212,6 @@
     margin: 0 0 16px;
     color: #50575e;
     font-size: 13px;
-    max-width: 720px;
 }
 
 /* ──────────────────────────────────────────────────────────────────
@@ -366,27 +371,12 @@
     border-top-color: #3c434a;
 }
 
-/* Auto — same dark rules behind prefers-color-scheme. Duplicated rather
-   than nested in @media-inside-selector (CSS doesn't allow that), kept
-   line-for-line in sync with the .radio-theme-dark block above. */
-@media (prefers-color-scheme: dark) {
-    .radio-theme-auto .radio-player__now { border-bottom-color: #3c434a; }
-    .radio-theme-auto .radio-player__station-name { color: #f0f0f1; }
-    .radio-theme-auto .radio-player__label,
-    .radio-theme-auto .radio-player__station-genre,
-    .radio-theme-auto .radio-player__volume-pct,
-    .radio-theme-auto .radio-player__credit,
-    .radio-theme-auto .radio-player__mute,
-    .radio-theme-auto .radio-player__station-select label,
-    .radio-theme-auto .radio-player__volume .dashicons { color: #a7aaad; }
-    .radio-theme-auto .radio-player__mute:hover { color: #f0f0f1; }
-    .radio-theme-auto .radio-player__mute--muted { color: #ff8b8b; }
-    .radio-theme-auto .radio-player__station-desc,
-    .radio-theme-auto .radio-player__track,
-    .radio-theme-auto .radio-intro { color: #c3c4c7; }
-    .radio-theme-auto .radio-player__station-genre { background: rgba(255, 255, 255, 0.08); }
-    .radio-theme-auto .radio-player__error { background: rgba(179, 45, 46, 0.18); color: #ff9b9b; }
-    .radio-theme-auto .radio-about-card { background: #1d2327; border-color: #3c434a; color: #c3c4c7; }
-    .radio-theme-auto .radio-about-card h2 { background: #2c3338; color: #f0f0f1; border-bottom-color: #3c434a; }
-    .radio-theme-auto #radio_dashboard_widget .radio-player__credit { border-top-color: #3c434a; }
+/* Give the player its own dark surface when theme=dark so the dark text
+   has something to read against — WP postboxes don't follow our dark
+   choice, so without this the light text would sit on white. */
+.radio-theme-dark .radio-player {
+    background: #1d2327;
+    padding: 14px 16px;
+    border-radius: 3px;
+    border: 1px solid #3c434a;
 }