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/index.html

@@ -8,7 +8,7 @@
 </head>
 <body>
 <header>
-  <a class="logo" href="/" onclick="location.replace('/');return false">ani-web</a>
+  <a class="logo" href="/">ani-web</a>
   <form onsubmit="const q=document.getElementById('q').value.trim(); if(q) location='?q='+encodeURIComponent(q); return false">
     <input id="q" placeholder="search anime…" autocomplete="off">
   </form>
@@ -22,6 +22,7 @@
   </div>
 </header>
 <main id="main"><p class="muted">Search for an anime to get started.</p></main>
+<div id="toasts"></div>
 <script src="hls.min.js"></script>
 <script src="app.js"></script>
 </body>