feat(web): show profile picture avatar in game page header

Fetches /api/me with the stored fs_token and renders a 32px circular
avatar in hud-right. Shows the profile photo when set, or the first
letter of the username as initials otherwise. Hidden when not signed in.
Clicking the avatar navigates to /account.

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

solitaire_server/web/game.css

@@ -59,6 +59,25 @@ header {
 .hud-center { display: flex; gap: 20px; font-size: 14px; font-weight: 600; }
 .hud-right { display: flex; align-items: center; gap: 10px; }
 
+.hud-avatar-link { display: flex; align-items: center; text-decoration: none; }
+.hud-avatar-inner {
+    width: 32px;
+    height: 32px;
+    border-radius: 50%;
+    overflow: hidden;
+    border: 2px solid rgba(255,255,255,0.15);
+    background: var(--panel-hi);
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    font-size: 13px;
+    font-weight: 700;
+    color: var(--text-muted);
+    transition: border-color 120ms;
+}
+.hud-avatar-link:hover .hud-avatar-inner { border-color: var(--accent); }
+.hud-avatar-inner img { width: 100%; height: 100%; object-fit: cover; border-radius: 50%; }
+
 .logo { font-size: 16px; font-weight: 700; }
 .muted { color: var(--text-muted); font-size: 12px; }
 .home-link {