feat: implement seeking (FFmpeg -ss restart), fix lyrics sync with seekOffset

- AudioPlayer.seek() restarts FFmpeg with -ss parameter for actual seeking
- New POST /api/player/:botId/seek endpoint
- BotStatus includes seekOffset and playStartTime from server
- Frontend elapsed = seekOffset + (now - playStartedAt)
- Progress bar click now seeks to clicked position
- All timing actions use _resetTiming() helper with seekOffset
- Lyrics sync uses store.elapsed which includes seekOffset

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/src/components/Player.vue

@@ -74,6 +74,7 @@
 <script setup lang="ts">
 import { computed, ref, onMounted, onUnmounted } from 'vue';
 import { Icon } from '@iconify/vue';
+import axios from 'axios';
 import { usePlayerStore } from '../stores/player.js';
 import CoverArt from './CoverArt.vue';
 import Queue from './Queue.vue';
@@ -101,10 +102,10 @@ function formatTime(seconds: number): string {
 }
 
 function updateProgress() {
-  // Directly compute elapsed from raw values (bypass Vue reactivity)
   const bot = store.activeBot;
+  const seekOff = store.seekOffset;
   if (bot?.playing && !bot.paused && store.playStartedAt > 0) {
-    currentElapsed.value = (Date.now() - store.playStartedAt) / 1000;
+    currentElapsed.value = seekOff + (Date.now() - store.playStartedAt) / 1000;
   } else if (bot?.paused) {
     currentElapsed.value = store.pausedElapsed;
   }
@@ -117,17 +118,22 @@ function updateProgress() {
   rafId = requestAnimationFrame(updateProgress);
 }
 
-function onProgressClick(e: MouseEvent) {
+async function onProgressClick(e: MouseEvent) {
   const bar = progressBarRef.value;
-  if (!bar) return;
+  if (!bar || !store.activeBotId) return;
   const rect = bar.getBoundingClientRect();
   const ratio = Math.max(0, Math.min(1, (e.clientX - rect.left) / rect.width));
   const duration = currentSong.value?.duration ?? 0;
   const seekTime = ratio * duration;
-  // Can't seek server-side FFmpeg stream — show tooltip with target time
-  progressTooltipTime.value = `跳转不可用 (${formatTime(seekTime)})`;
-  progressTooltipVisible.value = true;
-  setTimeout(() => { progressTooltipVisible.value = false; }, 1500);
+
+  try {
+    await axios.post(`/api/player/${store.activeBotId}/seek`, { position: seekTime });
+    store.seekOffset = seekTime;
+    store.playStartedAt = Date.now();
+    store.pausedElapsed = 0;
+  } catch {
+    // ignore
+  }
 }
 
 function onProgressHover(e: MouseEvent) {