Left-align page content and expand nav width

Change layout alignment from center to flex-start on various pages to
left-align content. Also increase .nav-inner max-width to 900px and set
margin to 0 so navigation aligns with page content.

src/components/Nav.astro

@@ -60,12 +60,12 @@ function isActive(href: string, current: string): boolean {
     }
 
     .nav-inner {
-        max-width: 700px;
-        margin: 0 auto;
+        max-width: 900px;
+        margin: 0;
         display: flex;
         flex-wrap: wrap;
         align-items: center;
-        justify-content: center;
+        justify-content: flex-start;
         gap: var(--space-xs);
         font-size: 0.85rem;
     }