feat(0.5.0): track history + favourites with four search providers

Quietly log every track that scrolls past the player to a per-user
history (capped 500). A star button promotes the good ones to a
separate Favourites tab that doesn't age out. Each row has four
search-provider deep links so you can find the track on whichever
service you use.

Storage
  Two new user_meta keys (separate from radio_state so frequent
  inserts don't churn the player-state blob):
    - radio_history    — capped FIFO of last 500 played tracks
    - radio_favourites — uncapped user-starred list

New page: Radio → History
  - History tab: capped FIFO list, newest first.
  - Favourites tab: starred tracks (uncapped).
  - Each row: when (relative + full timestamp on hover) / station /
    artist — title / four search links / favourite-star toggle.
  - Filter by artist/title (live, client-side) + by station (dropdown).
  - Clear history button (favourites preserved).
  - Search providers: Spotify, YouTube, Apple Music, Bandcamp.
    Deep-link URLs only — no API keys, no third-party JS.

Auto-logging during playback
  fetchTrack (existing 30s SomaFM poll loop) now hands new tracks to
  logTrackIfNew → POST to wp_ajax_radio_log_track. Dedup client-side
  (lastLoggedSig) AND server-side (against last entry in user_meta).
  Junk filtered server-side: (unknown) artist, missing artist/title.

New AJAX endpoints
  - radio_log_track          (nonce radio_save_state — player pages)
  - radio_toggle_favourite   (nonce radio_history — history page only)
  - radio_clear_history      (nonce radio_history — history page only)

Files
  - radio.php (version, require new include, submenu page, asset
    enqueue hook adds radio_page_radio-history, three AJAX endpoints,
    three new localized strings)
  - inc/history.php (NEW — storage helpers + admin page renderer)
  - assets/css/radio.css (history table, toolbar, search-link pills,
    favourite star, dark-theme overrides)
  - assets/js/radio.js (logTrackIfNew wired into fetchTrack;
    bindHistoryPage handles filter/favourite/clear)
  - inc/about.php (history entry)
  - CHANGELOG.md (full entry)

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

assets/css/radio.css

@@ -453,3 +453,105 @@
     border-radius: 3px;
     border: 1px solid #3c434a;
 }
+
+/* ──────────────────────────────────────────────────────────────────
+ * History + Favourites page (v0.5.0)
+ * ─────────────────────────────────────────────────────────────── */
+
+.radio-history-wrap { max-width: 1100px; }
+
+.radio-tab-count {
+    color: #646970;
+    font-weight: 400;
+    margin-left: 2px;
+}
+
+.radio-history-toolbar {
+    display: flex;
+    gap: 10px;
+    align-items: center;
+    margin: 12px 0 16px;
+    flex-wrap: wrap;
+}
+
+.radio-history-toolbar input[type="search"] {
+    flex: 1 1 220px;
+    max-width: 360px;
+}
+.radio-history-toolbar select { max-width: 220px; }
+.radio-history-clear { margin-left: auto !important; }
+
+.radio-history-empty {
+    margin-top: 24px;
+    padding: 24px;
+    background: #fff;
+    border: 1px solid #c3c4c7;
+    color: #50575e;
+    font-style: italic;
+    text-align: center;
+}
+
+.radio-history-table { background: #fff; }
+.radio-history-table th,
+.radio-history-table td { padding: 10px 12px; vertical-align: middle; }
+.radio-history-table th.when,
+.radio-history-table th.station,
+.radio-history-table th.fav { white-space: nowrap; }
+.radio-history-table .when,
+.radio-history-table .station {
+    color: #646970; font-size: 12px; white-space: nowrap;
+}
+.radio-history-table .track { font-size: 14px; }
+.radio-history-table .track strong { color: #1d2327; }
+.radio-history-table .search { white-space: nowrap; }
+.radio-history-table .fav { text-align: center; width: 42px; }
+
+/* Search-link pills, brand-tinted on hover */
+.radio-search-link {
+    display: inline-block;
+    padding: 2px 8px;
+    margin-right: 4px;
+    font-size: 11px;
+    font-weight: 600;
+    border-radius: 10px;
+    text-decoration: none;
+    background: #e2e4e7;
+    color: #1d2327;
+    transition: background 0.15s ease, color 0.15s ease;
+}
+.radio-search-link:hover                 { background: #d0d3d6; }
+.radio-search-link--spotify:hover        { background: #1ed760; color: #000; }
+.radio-search-link--youtube:hover        { background: #ff0000; color: #fff; }
+.radio-search-link--apple:hover          { background: #fa57c1; color: #fff; }
+.radio-search-link--bandcamp:hover       { background: #629aa9; color: #fff; }
+
+/* Favourite star — grey by default, golden when starred */
+.radio-fav-btn {
+    background: none;
+    border: 0;
+    padding: 4px 6px;
+    cursor: pointer;
+    font-size: 18px;
+    line-height: 1;
+    color: #c3c4c7;
+    transition: transform 0.12s ease, color 0.12s ease;
+}
+.radio-fav-btn:hover { transform: scale(1.2); color: #f0b849; }
+.radio-fav-btn:focus { outline: 2px solid var(--wp-admin-theme-color, #2271b1); outline-offset: 1px; }
+.radio-fav-btn.is-fav { color: #f0b849; }
+.radio-fav-btn[disabled] { opacity: 0.5; cursor: progress; }
+
+/* Filtered-out rows hidden via JS */
+.radio-history-row.is-filtered { display: none; }
+
+/* Dark theme — history surfaces */
+.radio-theme-dark .radio-history-table { background: #1d2327; color: #c3c4c7; border-color: #3c434a; }
+.radio-theme-dark .radio-history-table th { background: #2c3338; color: #f0f0f1; border-bottom-color: #3c434a; }
+.radio-theme-dark .radio-history-table .track strong { color: #f0f0f1; }
+.radio-theme-dark .radio-history-table .when,
+.radio-theme-dark .radio-history-table .station { color: #a7aaad; }
+.radio-theme-dark .radio-search-link { background: #2c3338; color: #c3c4c7; }
+.radio-theme-dark .radio-history-empty { background: #1d2327; border-color: #3c434a; color: #c3c4c7; }
+.radio-theme-dark .radio-fav-btn { color: #50575e; }
+.radio-theme-dark .radio-fav-btn.is-fav,
+.radio-theme-dark .radio-fav-btn:hover { color: #f0b849; }