feat(web): wire @playNext on all SongCard call sites

Library / Search / History / Playlist now route the third action to
store.playNextSong. Home is unchanged (it doesn't use SongCard).

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

web/src/views/History.vue

@@ -20,6 +20,7 @@
         :index="i + 1"
         :active="store.currentSong?.id === song.id"
         @play="store.playSong(song)"
+        @playNext="store.playNextSong(song)"
         @add="store.addSong(song)"
       />
     </div>

web/src/views/Library.vue

@@ -36,6 +36,7 @@
           :index="i + 1"
           :active="store.currentSong?.id === song.id"
           @play="store.play(song.name, song.platform)"
+          @playNext="store.playNextSong(song)"
           @add="store.addToQueue(song.name, song.platform)"
         />
       </div>

web/src/views/Playlist.vue

@@ -32,6 +32,7 @@
           :index="i + 1"
           :active="store.currentSong?.id === song.id"
           @play="store.playSong(song)"
+          @playNext="store.playNextSong(song)"
           @add="store.addSong(song)"
         />
       </div>

web/src/views/Search.vue

@@ -28,6 +28,7 @@
         :index="i + 1"
         :active="store.currentSong?.id === song.id"
         @play="store.playSong(song)"
+        @playNext="store.playNextSong(song)"
         @add="store.addSong(song)"
       />
     </div>