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.html

@@ -40,6 +40,12 @@
                 <input type="checkbox" id="chk-draw3"> Draw 3
             </label>
             <button id="btn-theme" title="Switch card theme">Dark</button>
+            <a id="hud-avatar" href="/account" title="Account" class="hud-avatar-link" style="display:none">
+                <div class="hud-avatar-inner">
+                    <img id="hud-avatar-img" src="" alt="" style="display:none">
+                    <span id="hud-avatar-initials"></span>
+                </div>
+            </a>
         </div>
     </header>