ui: loading states, player failure overlay + retry, toasts, back nav, full history page with delete

Bundle 1-4+7 from PLAN.md: skeleton loaders, player Loading/Buffering/fatal overlay with Retry, action toasts, back-to-home crumb + logo fix, ?history full-history view with per-entry delete (GET /api/history?all=1, DELETE /api/history). 14/14 tests green.

static/login.html

@@ -16,9 +16,13 @@ input { width:100%; box-sizing:border-box; padding:.55rem .8rem; border-radius:8
 button { width:100%; margin-top:.4rem; padding:.55rem; border:0; border-radius:8px;
   background:var(--acc); color:#000; font-weight:600; cursor:pointer; }
 .err { color:#f87171; font-size:.85rem; margin:.6rem 0 0; min-height:1.2em; }
+.banner { position:fixed; top:1rem; left:50%; transform:translateX(-50%); background:var(--card);
+  border:1px solid var(--bd); border-radius:8px; padding:.4rem .9rem; color:var(--muted);
+  font-size:.85rem; }
 </style>
 </head>
 <body>
+<p class="banner" id="banner" hidden></p>
 <form onsubmit="event.preventDefault(); login()">
   <h1>ani-web</h1>
   <input id="user" placeholder="username" autocomplete="username">
@@ -35,6 +39,11 @@ const BASE = (() => {
 })();
 const $ = id => document.getElementById(id);
 const next = new URLSearchParams(location.search).get("next");
+(() => {  // one-shot confirmations for logout / account delete
+  const s = new URLSearchParams(location.search);
+  const note = s.get("signedout") ? "Signed out." : s.get("deleted") ? "Account deleted." : null;
+  if (note) { const b = $("banner"); b.textContent = note; b.hidden = false; }
+})();
 async function login() {
   $("err").textContent = "";
   const r = await fetch(BASE + "login", {method: "POST",