feat: implement server password login, YouTube source, and improved bot selector UI

- **TS server password** (#7/#9): add serverPassword field across database,
  manager, bot API, and Settings UI — allows joining password-protected servers
- **YouTube audio source** (#1/#10): new YouTubeProvider using yt-dlp binary;
  adds -y flag in chat commands, /api/music supports platform=youtube,
  YouTube badge in SongCard, yt-dlp-wrap npm dependency
- **Bot selector UI** (#14): selector always visible (not just when >1 bot),
  bigger button with border and play-state indicator; per-bot URL routing at
  /bot/:id with BotRedirect view; copy-link button in dropdown

Closes #1, #7, #9, #10, #14

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/views/BotRedirect.vue

@@ -0,0 +1,42 @@
+<template>
+  <div class="redirect-page">
+    <span v-if="notFound">机器人不存在或未加载</span>
+    <span v-else>正在跳转...</span>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { onMounted, ref } from 'vue';
+import { useRoute, useRouter } from 'vue-router';
+import { usePlayerStore } from '../stores/player.js';
+
+const route = useRoute();
+const router = useRouter();
+const store = usePlayerStore();
+const notFound = ref(false);
+
+onMounted(async () => {
+  const botId = route.params.id as string;
+  if (!store.bots.length) {
+    await store.fetchBots();
+  }
+  const bot = store.bots.find((b) => b.id === botId);
+  if (bot) {
+    store.setActiveBotId(botId);
+    router.replace('/');
+  } else {
+    notFound.value = true;
+  }
+});
+</script>
+
+<style scoped>
+.redirect-page {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  height: 60vh;
+  font-size: 16px;
+  color: var(--text-secondary);
+}
+</style>