feat: v0.2.0 — UI rebuilt to WordPress admin standards

v0.1.0 worked but felt like a third-party React widget bolted on
top of WordPress. v0.2.0 makes the player visually native to the
WP admin: postbox container, standard Play/Pause button with text
label, admin-colour-scheme aware accents, dashboard widget no
longer renders a card inside a card.

CHANGES
- inc/admin-page.php: main page now wraps the player in a
  .postbox > .postbox-header (with h2.hndle) > .inside structure.
  Custom rounded card / shadow stripped.
- inc/dashboard-widget.php: bare .radio-player content; WP already
  wraps dashboard widgets in a postbox, was double-card before.
- inc/about.php: version-history card promotes v0.2.0 to latest,
  demotes v0.1.0.
- assets/css/radio.css: rewrite. Strip custom shadows + oversized
  typography. Adopt WP body-text defaults. Use
  var(--wp-admin-theme-color, #2271b1) for volume-slider accent +
  link colours so the plugin picks up whichever admin colour
  scheme the user has chosen. About-page cards now use the
  postbox-style gray header + 1px border pattern.
- assets/js/radio.js: setPlayIcon() also flips the visible text
  label ("Play" ↔ "Pause"), not just the icon class. mirrorSelection()
  also updates the [data-radio-genre] element so the genre label
  stays in sync across surfaces.
- radio.php: Version: 0.1.0 -> 0.2.0; BUDDY_VERSION constant
  bumped likewise.
- CHANGELOG.md: new [0.2.0] entry explaining the visual overhaul.

NET EFFECT
- Same 44 stations, same audio path, same persistence, same
  updater, same AJAX endpoint. Pure visual change.
- The plugin now looks like part of WordPress admin instead of a
  guest widget.
- Closer to WP.org submission criteria — plugin reviewers look
  for native-styled plugins.

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

inc/about.php

@@ -48,7 +48,11 @@ function radio_render_about_page() {
                 <h2><?php esc_html_e( 'Version history', 'radio' ); ?></h2>
                 <ul>
                     <li>
-                        <span class="ver">v0.1.0</span> &mdash; 26 May 2026 <span class="latest">latest</span><br>
+                        <span class="ver">v0.2.0</span> &mdash; 26 May 2026 <span class="latest">latest</span><br>
+                        <?php esc_html_e( 'UI rebuilt to WordPress admin standards. Postbox container, native Play/Pause button with text label, picks up your admin colour scheme via var(--wp-admin-theme-color), genre badge moved inline, dashboard widget no longer renders a card-inside-a-card. Functionality identical to v0.1.0 — purely visual polish.', 'radio' ); ?>
+                    </li>
+                    <li>
+                        <span class="ver">v0.1.0</span> &mdash; 26 May 2026<br>
                         <?php esc_html_e( 'First release. 44 SomaFM stations grouped by 10 genres, dashboard widget + dedicated admin page, per-user state in user_meta, self-hosted update checker against Gitea. Direct HTML5 audio playback — no proxy, no build step, no tracking.', 'radio' ); ?>
                     </li>
                 </ul>