Improve homepage Lighthouse performance

.htaccess

@@ -70,13 +70,13 @@ Options -Indexes
 </IfModule>
 
 # ----- Browser caching -----
-# No file-hashing on this site, so keep CSS/JS short (updates must propagate)
-# and cache images/fonts longer. HTML is always revalidated.
+# CSS/JS references carry a global content hash from tools/cache_bust.py, so
+# browsers can keep those immutable assets for a year. HTML is revalidated.
 <IfModule mod_expires.c>
     ExpiresActive On
     ExpiresByType text/html                    "access plus 0 seconds"
-    ExpiresByType text/css                     "access plus 1 day"
-    ExpiresByType application/javascript       "access plus 1 day"
+    ExpiresByType text/css                     "access plus 1 year"
+    ExpiresByType application/javascript       "access plus 1 year"
     ExpiresByType image/webp                   "access plus 1 month"
     ExpiresByType image/jpeg                   "access plus 1 month"
     ExpiresByType image/png                    "access plus 1 month"
@@ -86,6 +86,9 @@ Options -Indexes
 </IfModule>
 <IfModule mod_headers.c>
     Header set X-Content-Type-Options "nosniff"
+    <FilesMatch "\.(css|js)$">
+        Header set Cache-Control "public, max-age=31536000, immutable"
+    </FilesMatch>
     # HSTS: after the first HTTPS visit, browsers refuse plain HTTP for this
     # host. Conservative 6-month max-age, no preload/includeSubDomains so it
     # stays easy to adjust. (Ignored by browsers over plain HTTP — harmless.)