Content-hashed pkg assets (hash-files) so stale bundles can't pair with new wasm

An iPhone kept a heuristically-cached portal.js across three releases
(cached before Cache-Control: no-cache existed) and loaded it against
fresh wasm - its snippet imports 404'd, hydration never started, and
the gesture field never mounted. With hash-files = true every pkg
file is content-named and the freshly served page references exactly
its own bundle; hash.txt ships beside the binary (leptos resolves it
next to current_exe), the shell links the stylesheet through
HashedStylesheet, and instances set LEPTOS_HASH_FILES=true.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app.rs

@@ -1,5 +1,5 @@
 use leptos::prelude::*;
-use leptos_meta::{provide_meta_context, MetaTags, Stylesheet, Title};
+use leptos_meta::{provide_meta_context, HashedStylesheet, MetaTags, Title};
 use leptos_router::{
     components::{Route, Router, Routes},
     hooks::{use_location, use_navigate, use_query_map},
@@ -39,6 +39,9 @@ pub fn shell(options: LeptosOptions) -> impl IntoView {
                 // once loaded via <link>/<img> on Safari/iOS.
                 <link rel="icon" media="(prefers-color-scheme: light)" href="/favicon-light.svg" type="image/svg+xml"/>
                 <link rel="icon" media="(prefers-color-scheme: dark)" href="/favicon-dark.svg" type="image/svg+xml"/>
+                // Server-side, so it can read hash.txt and link the
+                // content-hashed stylesheet (hash-files = true).
+                <HashedStylesheet id="leptos" options=options.clone()/>
                 <AutoReload options=options.clone()/>
                 <HydrationScripts options/>
                 <MetaTags/>
@@ -67,7 +70,6 @@ pub fn App() -> impl IntoView {
     provide_context(site);
 
     view! {
-        <Stylesheet id="leptos" href="/pkg/portal.css"/>
         <Suspense fallback=|| ()>
             {move || {
                 site.get()