feat(0.6.0): pop-out mini-player — continuous background play across admin nav

Until v0.5.0 the audio cut every time you navigated between WP admin
pages — every navigation is a full page reload, which destroys the
<audio> element. v0.6.0 fixes the background-music use case by letting
you pop the player out into a separate browser window that persists
across the parent tab's navigation.

Pop-out window
  - Small "↗ Pop out" button beside the Play button on both the main
    Radio page and the Dashboard widget.
  - Opens a 380×560 standalone window via window.open() with a window
    name of `radio_popout` so a second click re-focuses the existing
    popup rather than spawning a new one.
  - Popup renders at admin-post.php?action=radio_popout&play=1 — a new
    admin_post_radio_popout hook outputs a full standalone HTML page
    (custom DOCTYPE / head / body, no WP admin chrome).
  - Theme follows radio_state['theme'] via body class radio-theme-{...}.
  - Includes the full player (now-playing block with dancing bars +
    Web Audio visualizer, play, mute, volume, station dropdown, error
    slot). Close button calls window.close().

Auto-resume + single-stream invariant
  - cfg.autoPlay is true when the popup URL carries &play=1. radio.js
    auto-calls audio.play() 200 ms after init. Same-origin user-gesture
    popups are exempt from autoplay-blocking on every modern browser.
  - On pop-out click, every other audio surface in the parent tab is
    paused so there is only ever one stream playing.

State stays in sync
  - Popup uses the SAME radio_save_state AJAX + track-logging endpoint.
    Station / volume changes persist to user_meta; track history keeps
    accumulating from whichever surface is playing.

Edge cases
  - Inside the popup, cfg.popoutUrl is '' so bindPopOut hides any
    Pop-out button it finds (would be infinite otherwise).
  - Popup blocked by browser → clear alert tells the user to allow
    popups for this site.

Files
  - radio.php (version, popoutUrl in localized config, admin_post
    handler + full standalone HTML renderer)
  - inc/admin-page.php + inc/dashboard-widget.php (Pop-out button
    beside Play)
  - assets/css/radio.css (.radio-player__popout styling)
  - assets/js/radio.js (bindPopOut function; autoPlay branch in
    bindPlayer)
  - inc/about.php + CHANGELOG.md (history entries)

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

CHANGELOG.md

@@ -9,6 +9,35 @@ Format: [Keep a Changelog 1.1.0](https://keepachangelog.com/en/1.1.0/) — versi
 
 ---
 
+## [0.6.0] — 2026-05-30 — Pop-out mini-player (continuous background play)
+
+Until v0.5.0 the audio cut every time you navigated between WP admin pages — every navigation is a full page reload, which destroys the `<audio>` element. v0.6.0 fixes the background-music use case by letting you pop the player out into a separate browser window that persists across the parent tab's navigation.
+
+### Added — **Pop out** button + standalone popup player
+- Small **`↗ Pop out`** button beside the Play button on both the main Radio page and the Dashboard widget. Click it and a **380×560 standalone window** opens with just the player chrome (no WP admin sidebar / nav).
+- The popup lives at `admin-post.php?action=radio_popout&play=1` — a new server-side route that renders a **full standalone HTML page** outside the WP admin shell (custom `<!DOCTYPE>`, head, body, no admin chrome).
+- Popup is `radio_popout`-named so a second click on Pop out **re-focuses the existing window** instead of opening a new one.
+- The popup's `<audio>` element is never destroyed by parent-tab navigation, so the music keeps playing while you click around Plugins, Posts, Users, etc.
+
+### Auto-resume — pick up where the main tab left off
+- The Pop-out button URL carries `&play=1`. `radio.js` reads it from the localized config and auto-calls `audio.play()` 200 ms after init. Same-origin user-gesture popups are exempt from autoplay-blocking on every modern browser, so it just works.
+- On opening the popup, **every other audio surface in the main tab is paused** so you don't end up with two streams running simultaneously.
+
+### Popup details
+- Theme follows the user's saved choice (`radio_state['theme']`) — light by default, dark if explicitly set; the popup body gets the `radio-theme-dark` class so the existing dark-mode CSS rules apply.
+- The popup includes everything you need to listen and switch: now-playing block (with dancing bars + Web Audio visualizer), play/pause, mute, volume, full station dropdown grouped by genre, error slot.
+- Close button (`✕`) in the top-right calls `window.close()`.
+- Pop out button **does not appear inside the popup** itself (would be infinite); the JS detects `popoutUrl === ''` in the localized config and hides any Pop-out button it finds.
+- Popup blocked? The button shows a clear alert: *"Pop-out blocked by the browser. Allow popups for this site, then try again."*
+
+### State stays in sync
+- The popup uses the **same `radio_save_state` AJAX endpoint** as the main player. If you change station or volume in the popup, it persists to user_meta; the next time you load any Radio page in the main tab it picks up the new values.
+- Track history continues to log from whichever surface is playing — the popup polls SomaFM and POSTs to `radio_log_track` exactly like the main player.
+
+**Files changed:** `radio.php` (version, `popoutUrl` added to localized config, new `admin_post_radio_popout` action + `radio_render_popout_page` handler with full standalone HTML), `inc/admin-page.php` + `inc/dashboard-widget.php` (Pop-out button beside Play), `assets/css/radio.css` (Pop-out button styling), `assets/js/radio.js` (`bindPopOut` opens the window + pauses other surfaces, autoplay branch reads `cfg.autoPlay`), `inc/about.php` (history entry).
+
+---
+
 ## [0.5.0] — 2026-05-29 — Track history + favourites
 
 SomaFM plays deep cuts you'll never hear again. v0.5.0 quietly logs every track that scrolls past so you can find it again later — and a star button keeps the ones worth keeping forever.