fix(call): mirror SSR node structure so the lobby call button hydrates

CallPanel's hydrate body wraps the join button in a dynamic child
(`{move || if in_call {..} else {button}}`), which serializes hydration
marker comments; the SSR body rendered a *static* button (plus a
`disabled=true` the hydrate button lacks). That structural mismatch meant
`on:click` never attached on the first lobby load — the call button was dead
until a client-side nav re-rendered the subtree. Mirror the dynamic-child
wrapper and the button's serialized attributes in the SSR branch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app.rs

@@ -472,19 +472,30 @@ fn CallPanel(room: Memo<String>, me: String) -> impl IntoView {
         }
             .into_any()
     }
-    // Must mirror the hydrate branch's default (not-in-call) markup exactly -
-    // hydration reconciles this SSR output against what the hydrate branch
-    // above expects to find, and an empty div here (vs. the button hydrate
-    // wants) is a hydration mismatch that panics and traps the whole wasm
-    // instance, killing all reactivity on the page.
+    // Must mirror the hydrate branch's default (not-in-call) markup AND its
+    // node structure exactly. The hydrate branch puts the button inside a
+    // dynamic child (`{move || ...}`), which serializes hydration-marker
+    // comments around it; if SSR emits a plain static button instead, the
+    // hydrate walk can't find the dynamic node, so it never attaches
+    // `on:click` - the call button is dead on the first lobby load until a
+    // client-side nav re-renders the subtree. So: same `{move || ...}` wrapper,
+    // and only the attributes the hydrate button actually serializes to
+    // (class/title/aria-label; `on:click` is a JS listener, not HTML). No
+    // `disabled` here - the hydrate button has none and hydration won't clear
+    // a stray SSR-only attribute.
     #[cfg(not(feature = "hydrate"))]
     {
         let _ = (room, me);
         view! {
             <div class="call-panel">
-                <button class="call-join" title="join call" aria-label="join call" disabled=true>
+                {move || {
+                    view! {
+                        <button class="call-join" title="join call" aria-label="join call">
                             "☎"
                         </button>
+                    }
+                        .into_any()
+                }}
             </div>
         }
             .into_any()