website: neutralise the six declarations that leak into the shell

shell.css loads after site.css, but later-wins is per PROPERTY, not per rule.
Where site.css declares something the controller's rule does not, the website's
value survives inside the shell. Measured: exactly six declarations, three
selectors, and the first one was visibly broken on the deployed page -

  .nav-links        display:flex + gap:32px -> the sidebar menu rendered as a
                    HORIZONTAL row spilling across the content column
  .lang-globe-menu  top + right -> fought the controller's bottom/left
  .page-header      padding + text-align -> the website's centred subpage header
                    fought the controller's left-aligned flex row

Reset in site.css, the website's own file, so shell.css stays a verbatim copy.
Found by diffing the two files' declaration sets per selector rather than by
spotting the one that happened to be visible.

website/404.html

@@ -6,7 +6,7 @@
     <title>Az oldal nem található | Felhom.eu</title>
     <meta name="robots" content="noindex, follow">
     <!-- shared assets: bump ?v= together on any site.css/icons.svg change -->
-    <link rel="stylesheet" href="/assets/site.css?v=14">
+    <link rel="stylesheet" href="/assets/site.css?v=16">
     <link rel="icon" type="image/png" href="/assets/logo_favicon_2.svg">
     <script defer src="https://stats.felhom.eu/script.js" data-website-id="d419db57-5e1c-48df-bdb3-c29f25fb1661"></script>
 </head>