Add a web player lyrics panel with active-line highlighting and click-to-seek

New GET /player/lyrics/{id} (auth-required) returns the best available
stored structuredLyrics entry for a song — preferring a synced one —
as plain JSON lines with a start time only where the source actually
has one.

The player bar gains a lyrics toggle; the panel fetches lyrics on
every song change, renders each line, and — only for lines that
actually carry a startMs — makes them clickable (seeks + plays) and
highlights the currently active line as playback progresses. Plain
(unsynced) lyrics render as static text with no fabricated timing or
highlighting.

Note: verified via Go template parsing/rendering and the new handler
tests, plus a JS syntax check; not manually exercised in a browser in
this session.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014r98AtcBbevpscWLsfwVvv

web/static/css/app.css

@@ -286,6 +286,44 @@ body {
   flex: 0 0 auto;
 }
 
+.vs-lyrics-panel {
+  position: fixed;
+  left: 0;
+  right: 0;
+  bottom: var(--vs-player-height);
+  max-height: 40vh;
+  overflow-y: auto;
+  background: var(--bs-body-bg);
+  border-top: 1px solid var(--bs-border-color);
+  padding: 1rem;
+  z-index: 1029;
+  text-align: center;
+}
+
+.vs-lyrics-line {
+  padding: 0.15rem 0;
+  color: var(--bs-secondary-color);
+  transition: color 0.15s ease;
+}
+
+.vs-lyrics-line.vs-lyrics-synced {
+  cursor: pointer;
+}
+
+.vs-lyrics-line.vs-lyrics-synced:hover {
+  color: var(--bs-body-color);
+}
+
+.vs-lyrics-line.vs-lyrics-active {
+  color: var(--bs-body-color);
+  font-weight: 600;
+}
+
+.vs-lyrics-empty {
+  color: var(--bs-secondary-color);
+  font-size: 0.85rem;
+}
+
 /* --- Misc --- */
 
 .vs-star-btn {

web/static/js/app.js

@@ -51,6 +51,7 @@
     this.ui.starBtn.dataset.itemId = song.id;
     this.ui.starBtn.classList.toggle("active", !!song.starred);
     this.ui.starBtn.innerHTML = song.starred ? '<i class="bi bi-star-fill"></i>' : '<i class="bi bi-star"></i>';
+    this._loadLyrics(song.id);
 
     if ("mediaSession" in navigator) {
       navigator.mediaSession.metadata = new MediaMetadata({
@@ -61,6 +62,79 @@
     }
   };
 
+  // --- Lyrics panel: fetches the real structured lyrics stored for the
+  // current song (internal/database.GetSongStructuredLyrics via
+  // /player/lyrics/{id}), renders them, and — only for lines that
+  // actually carry a start time — supports active-line highlighting and
+  // click-to-seek. Plain lyrics render as static text with no seek
+  // affordance, since there's no timing to seek to. ---
+
+  VibeSonicPlayer.prototype._loadLyrics = function (songId) {
+    var self = this;
+    this.lyricsLines = [];
+    if (!this.ui.lyricsPanel) return;
+    fetch("/player/lyrics/" + encodeURIComponent(songId))
+      .then(function (r) { return r.ok ? r.json() : null; })
+      .then(function (data) {
+        // Ignore a response that arrived after the user already skipped
+        // to a different song.
+        if (!data || (self.queue[self.index] || {}).id !== songId) return;
+        self.lyricsLines = data.lines || [];
+        self._renderLyrics();
+      })
+      .catch(function () {
+        self.lyricsLines = [];
+        self._renderLyrics();
+      });
+  };
+
+  VibeSonicPlayer.prototype._renderLyrics = function () {
+    var panel = this.ui.lyricsPanel;
+    if (!panel) return;
+    panel.textContent = "";
+    if (!this.lyricsLines.length) {
+      var empty = document.createElement("div");
+      empty.className = "vs-lyrics-empty";
+      empty.textContent = "No lyrics available for this song.";
+      panel.appendChild(empty);
+      return;
+    }
+    var self = this;
+    this.lyricsLines.forEach(function (line, i) {
+      var el = document.createElement("div");
+      el.className = "vs-lyrics-line";
+      el.textContent = line.text;
+      if (line.startMs != null) {
+        el.classList.add("vs-lyrics-synced");
+        el.dataset.startMs = String(line.startMs);
+        el.addEventListener("click", function () {
+          self.audio.currentTime = line.startMs / 1000;
+          self.audio.play().catch(function () {});
+        });
+      }
+      panel.appendChild(el);
+    });
+  };
+
+  VibeSonicPlayer.prototype._updateActiveLyricLine = function (curMs) {
+    var panel = this.ui.lyricsPanel;
+    if (!panel || !this.lyricsLines.length) return;
+    var activeIndex = -1;
+    for (var i = 0; i < this.lyricsLines.length; i++) {
+      var startMs = this.lyricsLines[i].startMs;
+      if (startMs != null && startMs <= curMs) activeIndex = i;
+    }
+    if (activeIndex === this._activeLyricIndex) return;
+    this._activeLyricIndex = activeIndex;
+    var nodes = panel.querySelectorAll(".vs-lyrics-line");
+    nodes.forEach(function (node, i) {
+      node.classList.toggle("vs-lyrics-active", i === activeIndex);
+    });
+    if (activeIndex >= 0 && !panel.classList.contains("d-none")) {
+      nodes[activeIndex].scrollIntoView({ block: "center", behavior: "smooth" });
+    }
+  };
+
   VibeSonicPlayer.prototype.playPause = function () {
     if (!this.queue.length) return;
     if (this.audio.paused) {
@@ -123,6 +197,7 @@
     if (dur > 0) {
       this.ui.progress.value = String((cur / dur) * 100);
     }
+    this._updateActiveLyricLine(cur * 1000);
   };
 
   function formatTime(seconds) {
@@ -165,9 +240,18 @@
       progress: document.getElementById("vs-progress"),
       volumeSlider: document.getElementById("vs-volume"),
       starBtn: document.getElementById("vs-now-star"),
+      lyricsPanel: document.getElementById("vs-lyrics-panel"),
     };
     var player = new VibeSonicPlayer(audio, ui);
 
+    var lyricsBtn = document.getElementById("vs-lyrics-btn");
+    if (lyricsBtn && ui.lyricsPanel) {
+      lyricsBtn.addEventListener("click", function () {
+        ui.lyricsPanel.classList.toggle("d-none");
+        lyricsBtn.classList.toggle("active");
+      });
+    }
+
     document.getElementById("vs-play-btn").addEventListener("click", function () {
       player.playPause();
     });