feat(0.3.0): dark theme, mute, media keys, current-track + 2nd-look fixes

Closes the gaps from a UI review of v0.2.0.

Added
- Mute toggle: speaker icon is now a button; remembers prior volume.
- MediaSession API: OS media keys / headphone buttons / lock-screen
  widget play/pause the radio. Metadata exposes station + SomaFM + genre.
- Current-track display: polls https://somafm.com/songs/{code}.json every
  30s while playing; shown as `♪ Title — Artist` under the description.
  Best-effort — silently hidden if CORS-blocked / unreachable.

Fixed (2nd-look)
- Dark theme now actually renders. v0.2.0 saved the dropdown but had no
  CSS — add `admin_body_class` filter + `radio-theme-{auto,light,dark}`
  CSS for the player + about-cards. `auto` follows OS prefers-color-scheme.
- Settings-page volume slider: removed inline `oninput`; wired in radio.js
  via `bindSettingsSlider()`. Cleaner under strict CSP.
- Save errors surface as a transient notice instead of being swallowed.
- Gitea changelog URL moved into `RADIO_GITEA_URL` constant.
- Genre badge restyled as an inline pill (was using `margin-left: auto`
  which wrapped poorly on narrow widget widths).

Files
- radio.php (version, constant, strings, body-class filter)
- inc/about.php (use constant, add 0.3.0 history entry)
- inc/settings.php (drop inline oninput)
- inc/admin-page.php + inc/dashboard-widget.php (mute button, track slot)
- assets/css/radio.css (pill, mute, track, dark-theme rules)
- assets/js/radio.js (rewrite: mute, MediaSession, track polling,
  settings slider, save-error surfacing)

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

CHANGELOG.md

@@ -9,6 +9,32 @@ Format: [Keep a Changelog 1.1.0](https://keepachangelog.com/en/1.1.0/) — versi
 
 ---
 
+## [0.3.0] — 2026-05-29 — Dark theme + mute + media keys + current-track display
+
+A polish pass that closes the gaps surfaced by a UI review. Two categories: **2nd-look fixes** (things the previous release implied but didn't actually deliver) and **nice-to-haves** (small upgrades that lift the admin-player feel).
+
+### Added — features
+- **Mute toggle on the speaker icon.** The icon next to the volume slider is now a button. Click to mute (icon flips to `dashicons-controls-volumeoff`, tinted red); click again to restore the prior volume. Remembers volume across mute/unmute via `data-prev-volume`.
+- **MediaSession API integration.** OS media keys (F8/F9 on Mac, Bluetooth headphone buttons, lock-screen widget on supported platforms) now play/pause the radio. The currently-playing station name, "SomaFM" as artist, and the genre as album are exposed as `MediaMetadata` so they show on the OS overlays.
+- **Current-track display.** Polls `https://somafm.com/songs/{code}.json` every 30 seconds **while playing only** and shows the track as `♪ Title — Artist` under the station description. Best-effort: silently hidden if the endpoint is unreachable / CORS-blocked, so the plugin keeps working regardless.
+
+### Fixed — 2nd-look
+- **Dark theme is now actually wired through.** v0.2.0 saved the Theme dropdown (auto / light / dark) but had no CSS to render anything other than light. v0.3.0 adds `admin_body_class` filter → `radio-theme-{auto,light,dark}` body class → corresponding dark-palette CSS for the player + about-cards. `auto` follows the OS via `prefers-color-scheme: dark`.
+- **Settings-page volume slider** no longer uses an inline `oninput=""` handler — the listener moved into `assets/js/radio.js` (`bindSettingsSlider`). Cleaner under strict-CSP environments.
+- **Save errors are surfaced.** AJAX state-save failures were previously swallowed silently — the local UI updated but the user had no signal if the server dropped the request. The plugin now shows a brief notice ("Preferences not saved — check your connection.") in the player's error slot for 3.5 s, then auto-clears.
+- **Hardcoded Gitea URL** in the About page replaced with a `RADIO_GITEA_URL` constant defined in `radio.php`. One place to update if the repo ever moves.
+- **Genre badge layout fix.** Was using `margin-left: auto` inside a wrap-enabled flex row, which caused it to land on its own line on narrow widget widths. Now styled as a small inline pill (rounded `rgba(0,0,0,0.06)` background) that flows naturally next to the station name.
+
+### Other
+- Plugin version bumped to **0.3.0**.
+- New localized strings: `mute`, `unmute`, `saveError` (for the JS-driven UI).
+- The mute button has a visible focus ring (`outline: 2px solid var(--wp-admin-theme-color)`) for keyboard navigation.
+- Volume slider input now also exits mute state (sets `audio.muted = false` on drag), so dragging the slider always overrides a prior mute click.
+
+**Files changed:** `radio.php` (version, constant, strings, `admin_body_class` filter), `inc/about.php` (constant for changelog URL), `inc/settings.php` (removed inline `oninput`), `inc/admin-page.php` + `inc/dashboard-widget.php` (speaker icon → mute button, added track slot), `assets/css/radio.css` (genre badge pill, mute button, track display, dark-theme rules incl. `prefers-color-scheme` for `auto`), `assets/js/radio.js` (full rewrite incl. `bindMute`, `bindSettingsSlider`, `startTrackPolling`/`stopTrackPolling`, `updateMediaSession`, save-error surfacing).
+
+---
+
 ## [0.2.0] — 2026-05-26
 
 ### Changed — UI rebuilt to WordPress admin standards