feat: add user support with play event tracking

Backend (Rust API):
- Add users and play_events tables (migration 0005)
- Extract full user identity from JWT (sub, username, email, name)
  and pass AuthUser via request extensions to all handlers
- Auto-upsert user in background on every authenticated request
- POST /api/tracks/:slug/play endpoint to record play events
- Allow POST method in CORS

Frontend (Node player):
- Call recordPlay() when a track starts playing
- Add user profile avatar with dropdown menu (name, email, sign out)
- Pass user info from App through FurumiPlayer to Header

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

furumi-node-player/client/src/furumiApi.ts

@@ -80,6 +80,10 @@ export async function getTrackInfo(trackSlug: string): Promise<TrackDetail | nul
   return res?.data ?? null
 }
 
+export async function recordPlay(trackSlug: string): Promise<void> {
+  await furumiApi.post(`/tracks/${trackSlug}/play`).catch(() => null)
+}
+
 export async function preloadStream(trackSlug: string) {
   return await furumiApi.get(`/stream/${trackSlug}`, { responseType: 'blob' }).catch(() => null)
 }