tests: fix rAF-stall flakes in headless chromium; login form submits on Enter

Headless Chromium 151 stops generating animation frames on idle pages,
which stalls Playwright's rAF-based waits (wait_for_function default
polling, click actionability 'stable' check). Fixes:
- wait_for_function: explicit timer polling (100ms/250ms)
- video readyState wait: 120s (cold upstream/CDN starts)
- .card click: force=True
- login: form submit handler (Enter key works, was button-only)
- test asserts the seeded entry, not a section header that only
  appeared via an API-test side effect

static/login.html

@@ -19,7 +19,7 @@ button { width:100%; margin-top:.4rem; padding:.55rem; border:0; border-radius:8
 </style>
 </head>
 <body>
-<form onsubmit="return false">
+<form onsubmit="event.preventDefault(); login()">
   <h1>ani-web</h1>
   <input id="user" placeholder="username" autocomplete="username">
   <input type="password" id="pw" placeholder="password" autocomplete="current-password">
@@ -35,7 +35,7 @@ const BASE = (() => {
 })();
 const $ = id => document.getElementById(id);
 const next = new URLSearchParams(location.search).get("next");
-$("go").onclick = async () => {
+async function login() {
   $("err").textContent = "";
   const r = await fetch(BASE + "login", {method: "POST",
     headers: {"Content-Type": "application/json"},
@@ -45,7 +45,7 @@ $("go").onclick = async () => {
   } else {
     $("err").textContent = (await r.json().catch(() => ({}))).detail || "login failed";
   }
-};
+}
 </script>
 </body>
 </html>