music: nightly 3am full reindex (staged + atomic swap)

Self-scheduling timer in the sidecar (fresh setTimeout each night, so it always
fires at 3am local regardless of drift) runs reindexFull() — builds into a fresh
slot and swaps atomically only on success, never disrupting the live index.
Started at boot, cleared on shutdown. Logs the next scheduled time + each run.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/servers/sidecar/music/index.ts

@@ -3,6 +3,7 @@ import { join } from 'node:path';
 import type { SidecarCommand, SidecarEvent } from '../protocol';
 import { createSidecarConnector } from '../connect';
 import { streamAudioFile } from './stream-audio';
+import { startNightlyReindex, stopNightlyReindex } from './nightly-reindex';
 import {
   reindexNow,
   ensureCacheSetup,
@@ -74,6 +75,9 @@ const port = getFreePort();
 // Ensure the cache is a symlink-to-slot before serving/building, so full reindexes can swap atomically.
 await ensureCacheSetup();
 
+// Nightly full reindex at 3am (staged + atomic swap).
+startNightlyReindex();
+
 const server = Bun.serve({
   port,
   hostname: '127.0.0.1',
@@ -267,6 +271,7 @@ const connection = createSidecarConnector({
 
 function shutdown(signal: string) {
   console.log(`[music] ${signal} received, shutting down...`);
+  stopNightlyReindex();
   try {
     server.stop(true);
   } catch {