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/components/header/Header.tsx

@@ -1,3 +1,4 @@
+import { useState, useRef, useEffect } from 'react'
 import { SearchDropdown } from '../SearchDropdown'
 import styles from './header.module.css'
 
@@ -8,16 +9,61 @@ type SearchResultItem = {
   detail?: string
 }
 
+type UserInfo = {
+  sub: string
+  name?: string
+  email?: string
+}
+
 type HeaderProps = {
   searchOpen: boolean
   searchResults: SearchResultItem[]
   onSearchSelect: (type: string, slug: string) => void
+  user: UserInfo
+}
+
+function UserMenu({ user }: { user: UserInfo }) {
+  const [open, setOpen] = useState(false)
+  const ref = useRef<HTMLDivElement>(null)
+
+  useEffect(() => {
+    function handleClick(e: MouseEvent) {
+      if (ref.current && !ref.current.contains(e.target as Node)) setOpen(false)
+    }
+    document.addEventListener('mousedown', handleClick)
+    return () => document.removeEventListener('mousedown', handleClick)
+  }, [])
+
+  const initials = (user.name ?? user.sub)
+    .split(' ')
+    .map((w) => w[0])
+    .slice(0, 2)
+    .join('')
+    .toUpperCase()
+
+  return (
+    <div className={styles.userMenu} ref={ref}>
+      <button className={styles.userAvatar} onClick={() => setOpen(!open)} title={user.name ?? user.sub}>
+        {initials}
+      </button>
+      {open && (
+        <div className={styles.userDropdown}>
+          <div className={styles.userInfo}>
+            <div className={styles.userName}>{user.name ?? user.sub}</div>
+            {user.email && <div className={styles.userEmail}>{user.email}</div>}
+          </div>
+          <a href="/auth/logout" className={styles.userLogout}>Sign out</a>
+        </div>
+      )}
+    </div>
+  )
 }
 
 export function Header({
   searchOpen,
   searchResults,
   onSearchSelect,
+  user,
 }: HeaderProps) {
   return (
     <header className={styles.header}>
@@ -40,6 +86,7 @@ export function Header({
             onSelect={onSearchSelect}
           />
         </div>
+        <UserMenu user={user} />
       </div>
     </header>
   )