feat: play real music from local library in Memories slideshow

Scans MUSIC_DIR (mounted at /music in Docker) with music-metadata to
read embedded BPM/genre tags and classify tracks as upbeat/cinematic/
dreamy. Falls back to untagged general pool when mood bucket is thin.
Slideshow plays real audio via <audio> element with range-request
streaming; Web Audio synth is kept as fallback when MUSIC_DIR is unset.
Shows now-playing title/artist in the slideshow bottom bar.

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

worker/scanMusic.js

@@ -0,0 +1,95 @@
+import fs from 'fs';
+import path from 'path';
+import { parseFile } from 'music-metadata';
+
+const AUDIO_EXTS = new Set(['.mp3', '.flac', '.m4a', '.ogg', '.wav', '.aac', '.opus', '.wma']);
+
+// Genre keywords → mood (case-insensitive substring match, first hit wins)
+const UPBEAT_KEYS = ['rock', 'pop', 'dance', 'electronic', 'hip hop', 'hip-hop', 'r&b', 'rnb',
+                     'reggae', 'funk', 'disco', 'punk', 'metal', 'latin', 'techno', 'house',
+                     'edm', 'trap', 'country'];
+const DREAMY_KEYS = ['ambient', 'classical', 'chill', 'lounge', 'jazz', 'new age', 'folk',
+                     'acoustic', 'meditation', 'sleep', 'indie folk', 'singer-songwriter', 'blues',
+                     'orchestral', 'soundtrack', 'cinematic'];
+
+function classifyMood(bpm, genre) {
+  if (bpm != null) {
+    if (bpm >= 120) return 'upbeat';
+    if (bpm >= 80)  return 'cinematic';
+    return 'dreamy';
+  }
+  if (genre) {
+    const g = genre.toLowerCase();
+    if (UPBEAT_KEYS.some(k => g.includes(k))) return 'upbeat';
+    if (DREAMY_KEYS.some(k => g.includes(k))) return 'dreamy';
+    return 'cinematic';
+  }
+  return 'general'; // no tags — all moods can use
+}
+
+function* walkDir(dir) {
+  let entries;
+  try { entries = fs.readdirSync(dir, { withFileTypes: true }); }
+  catch { return; }
+  for (const e of entries) {
+    const full = path.join(dir, e.name);
+    if (e.isDirectory()) yield* walkDir(full);
+    else if (AUDIO_EXTS.has(path.extname(e.name).toLowerCase())) yield full;
+  }
+}
+
+export let musicScanActive = false;
+
+export function initMusicTable(db) {
+  db.raw.exec(`
+    CREATE TABLE IF NOT EXISTS music (
+      id         INTEGER PRIMARY KEY AUTOINCREMENT,
+      filepath   TEXT NOT NULL UNIQUE,
+      title      TEXT,
+      artist     TEXT,
+      album      TEXT,
+      bpm        REAL,
+      genre      TEXT,
+      duration   REAL,
+      mood       TEXT NOT NULL DEFAULT 'general',
+      scanned_at TEXT NOT NULL DEFAULT (datetime('now'))
+    );
+    CREATE INDEX IF NOT EXISTS idx_music_mood ON music(mood);
+  `);
+}
+
+export async function scanMusicLibrary(musicDir, db) {
+  if (musicScanActive) return 0;
+  musicScanActive = true;
+  initMusicTable(db);
+
+  const hasTrack = db.raw.prepare('SELECT 1 FROM music WHERE filepath = ? LIMIT 1');
+  const insert   = db.raw.prepare(`
+    INSERT OR IGNORE INTO music (filepath, title, artist, album, bpm, genre, duration, mood)
+    VALUES (@filepath, @title, @artist, @album, @bpm, @genre, @duration, @mood)
+  `);
+
+  let added = 0;
+  try {
+    for (const fp of walkDir(path.resolve(musicDir))) {
+      if (hasTrack.get(fp)) continue;
+      try {
+        const { common, format } = await parseFile(fp, { duration: true, skipCovers: true });
+        const bpm   = common.bpm ?? null;
+        const genre = common.genre?.[0] ?? null;
+        insert.run({
+          filepath: fp,
+          title:    common.title  ?? path.basename(fp, path.extname(fp)),
+          artist:   common.artist ?? null,
+          album:    common.album  ?? null,
+          bpm, genre, duration: format.duration ?? null,
+          mood: classifyMood(bpm, genre),
+        });
+        added++;
+      } catch {}
+    }
+  } finally {
+    musicScanActive = false;
+  }
+  return added;
+}