Complete Phase 4: security hardening, player/playlist/admin UI, docs

Security:
- New internal/netguard package: podcast feed/enclosure fetching now
  refuses to dial non-public IPs (loopback/RFC1918/link-local/cloud
  metadata/CGNAT), validated per-connection including across redirects,
  closing an SSRF gap where a malicious or compromised feed URL could
  probe the server's internal network. Configurable via
  VIBESONIC_PODCASTS_ALLOW_PRIVATE_NETWORKS for intentional LAN feeds.
- Podcast episode downloads capped at 4GB (was unbounded, disk-exhaustion risk)
- Cover art decoding now rejects images above a 40-megapixel budget
  before full decode (decompression-bomb guard)
- HTTP server sets ReadHeaderTimeout (slowloris hardening)
- Admin folder-scan redirect now validated as same-site instead of
  trusting the raw Referer header (open-redirect fix)
- Legacy Subsonic token/salt auth now uses a constant-time comparison

Web UI completion:
- Persistent player: shuffle and repeat (off/all/one) controls, wired
  into queue advance/prev logic and persisted like other player state
- Admin user-permissions form: adminRole toggle (with a guard against
  demoting the last remaining admin) and per-user music-folder access
  checkboxes, backed by existing schema/enforcement that was previously
  unreachable from the UI
- Playlist M3U8 import/export

Docs: added docs/client-compatibility.md (honest tracking template —
no client testing has been performed), docs/deployment.md,
docs/security.md, docs/backup.md; refreshed README and cross-links;
added a footnote in docs/subsonic-compatibility.md distinguishing
spec-standard from VibeSonic-original OpenSubsonic extensions.

Also added Go fuzz tests for the external-auth CIDR/IP parser and the
LRC lyrics parser.

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

web/static/css/app.css

@@ -262,6 +262,10 @@ body {
   font-size: 1.4rem;
 }
 
+.vs-player-btn.active {
+  color: var(--bs-primary);
+}
+
 .vs-player-timeline {
   display: flex;
   align-items: center;

web/static/js/app.js

@@ -26,9 +26,20 @@
     this.ui = ui;
     this.queue = [];
     this.index = -1;
+    this.shuffle = false;
+    this.repeat = "off"; // "off" | "all" | "one"
+    this.shuffleOrder = []; // permutation of queue indices; shufflePos points into it
+    this.shufflePos = -1;
+    try {
+      this.shuffle = localStorage.getItem("vs-shuffle") === "1";
+      var storedRepeat = localStorage.getItem("vs-repeat");
+      if (storedRepeat === "all" || storedRepeat === "one") this.repeat = storedRepeat;
+    } catch (e) {
+      /* storage may be unavailable (private browsing); state just won't persist */
+    }
     this.audio.addEventListener("timeupdate", this._onTimeUpdate.bind(this));
     this.audio.addEventListener("loadedmetadata", this._onTimeUpdate.bind(this));
-    this.audio.addEventListener("ended", this.next.bind(this));
+    this.audio.addEventListener("ended", this._onEnded.bind(this));
     this.audio.addEventListener("play", this._syncPlayIcon.bind(this));
     this.audio.addEventListener("pause", this._syncPlayIcon.bind(this));
   }
@@ -36,10 +47,68 @@
   VibeSonicPlayer.prototype.playQueue = function (songs, startIndex) {
     this.queue = songs;
     this.index = startIndex || 0;
+    this._reshuffle();
     this._loadCurrent();
     this.audio.play().catch(function () {});
   };
 
+  // _reshuffle rebuilds the shuffle order (a Fisher-Yates permutation of
+  // every queue index except the currently-playing one, which is pinned
+  // to the front) whenever the queue changes or shuffle is toggled on,
+  // so "next" has a fresh random order to draw from without immediately
+  // repeating the track that's already playing.
+  VibeSonicPlayer.prototype._reshuffle = function () {
+    var order = [];
+    for (var i = 0; i < this.queue.length; i++) {
+      if (i !== this.index) order.push(i);
+    }
+    for (var j = order.length - 1; j > 0; j--) {
+      var k = Math.floor(Math.random() * (j + 1));
+      var tmp = order[j];
+      order[j] = order[k];
+      order[k] = tmp;
+    }
+    order.unshift(this.index);
+    this.shuffleOrder = order;
+    this.shufflePos = 0;
+  };
+
+  VibeSonicPlayer.prototype.setShuffle = function (on) {
+    this.shuffle = on;
+    try {
+      localStorage.setItem("vs-shuffle", on ? "1" : "0");
+    } catch (e) {}
+    if (on) this._reshuffle();
+    if (this.ui.shuffleBtn) this.ui.shuffleBtn.classList.toggle("active", on);
+  };
+
+  VibeSonicPlayer.prototype.cycleRepeat = function () {
+    this.repeat = this.repeat === "off" ? "all" : this.repeat === "all" ? "one" : "off";
+    try {
+      localStorage.setItem("vs-repeat", this.repeat);
+    } catch (e) {}
+    this._syncRepeatButton();
+  };
+
+  VibeSonicPlayer.prototype._syncRepeatButton = function () {
+    var btn = this.ui.repeatBtn;
+    if (!btn) return;
+    btn.dataset.repeat = this.repeat;
+    btn.classList.toggle("active", this.repeat !== "off");
+    var icon = btn.querySelector("i");
+    if (icon) icon.className = this.repeat === "one" ? "bi bi-repeat-1" : "bi bi-repeat";
+    btn.title = this.repeat === "off" ? "Repeat: off" : this.repeat === "all" ? "Repeat: all" : "Repeat: one";
+  };
+
+  VibeSonicPlayer.prototype._onEnded = function () {
+    if (this.repeat === "one") {
+      this.audio.currentTime = 0;
+      this.audio.play().catch(function () {});
+      return;
+    }
+    this.next();
+  };
+
   VibeSonicPlayer.prototype._loadCurrent = function () {
     var song = this.queue[this.index];
     if (!song) return;
@@ -145,11 +214,25 @@
   };
 
   VibeSonicPlayer.prototype.next = function () {
-    if (this.index + 1 < this.queue.length) {
+    if (!this.queue.length) return;
+    if (this.shuffle) {
+      if (this.shufflePos + 1 < this.shuffleOrder.length) {
+        this.shufflePos++;
+      } else if (this.repeat === "all") {
+        this._reshuffle();
+      } else {
+        return;
+      }
+      this.index = this.shuffleOrder[this.shufflePos];
+    } else if (this.index + 1 < this.queue.length) {
       this.index++;
-      this._loadCurrent();
-      this.audio.play().catch(function () {});
+    } else if (this.repeat === "all") {
+      this.index = 0;
+    } else {
+      return;
     }
+    this._loadCurrent();
+    this.audio.play().catch(function () {});
   };
 
   VibeSonicPlayer.prototype.prev = function () {
@@ -157,11 +240,17 @@
       this.audio.currentTime = 0;
       return;
     }
-    if (this.index > 0) {
+    if (this.shuffle) {
+      if (this.shufflePos <= 0) return;
+      this.shufflePos--;
+      this.index = this.shuffleOrder[this.shufflePos];
+    } else if (this.index > 0) {
       this.index--;
-      this._loadCurrent();
-      this.audio.play().catch(function () {});
+    } else {
+      return;
     }
+    this._loadCurrent();
+    this.audio.play().catch(function () {});
   };
 
   VibeSonicPlayer.prototype.seekTo = function (fraction) {
@@ -241,8 +330,23 @@
       volumeSlider: document.getElementById("vs-volume"),
       starBtn: document.getElementById("vs-now-star"),
       lyricsPanel: document.getElementById("vs-lyrics-panel"),
+      shuffleBtn: document.getElementById("vs-shuffle-btn"),
+      repeatBtn: document.getElementById("vs-repeat-btn"),
     };
     var player = new VibeSonicPlayer(audio, ui);
+    player.setShuffle(player.shuffle);
+    player._syncRepeatButton();
+
+    if (ui.shuffleBtn) {
+      ui.shuffleBtn.addEventListener("click", function () {
+        player.setShuffle(!player.shuffle);
+      });
+    }
+    if (ui.repeatBtn) {
+      ui.repeatBtn.addEventListener("click", function () {
+        player.cycleRepeat();
+      });
+    }
 
     var lyricsBtn = document.getElementById("vs-lyrics-btn");
     if (lyricsBtn && ui.lyricsPanel) {