fix(website): set content container width to 800px on desktop

Move the 800px max-width from .markdown-body up to .content so
the entire content pane (not just the inner body) is sized
correctly. The container now fills up to 800px beside the sidebar.

Author: claude

internal/website/_layouts/default.html

@@ -36,8 +36,8 @@
     .sidebar li { margin:.35rem 0; }
     .sidebar a { color:#222; display:block; padding:.25rem .4rem; border-radius:4px; }
     .sidebar a:hover { background:#f2f5f8; }
-    .content { flex:1; min-width:0; padding:2rem 2.5rem; }
-    .content .markdown-body { max-width: 800px; }
+    .content { flex:1; min-width:0; max-width: 800px; padding:2rem 2.5rem; }
+    .content .markdown-body { max-width: 100%; }
     pre, code { font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace; }
     pre { background:#f6f8fa; border:1px solid #d0d7de; padding:.9rem 1rem; border-radius:6px; overflow-x:auto; max-width:100%; }
     code { word-wrap: break-word; }