Add Nav, About/Projects pages and nginx hardening

Harden nginx: add CSP, HSTS, Referrer-Policy and Permissions-Policy;
include image/svg+xml in gzip types; set X-Content-Type-Options on
static assets; change try_files to return =404.

Add Nav component and wire into BaseLayout; add About and Projects
pages with projects.json, an initial blog post, and small layout/padding
adjustments (removed redundant back links).

src/pages/blog/index.astro

@@ -19,7 +19,6 @@ function formatDate(date: Date) {
     <main class="main">
         <div class="container">
             <header class="header fade-in">
-                <p class="back"><a href="/">← back to home</a></p>
                 <h1 class="title">Blog</h1>
                 <div class="divider">══════════════════════════════</div>
             </header>
@@ -45,7 +44,6 @@ function formatDate(date: Date) {
             )}
 
             <footer class="footer fade-in">
-                <div class="divider">══════════════════════════════</div>
                 <p>Made with love by Latte</p>
             </footer>
         </div>
@@ -79,6 +77,7 @@ function formatDate(date: Date) {
         align-items: center;
         justify-content: center;
         padding: var(--space-lg) var(--space-md);
+        padding-top: calc(var(--space-lg) + 3rem);
     }
 
     .container {
@@ -95,19 +94,6 @@ function formatDate(date: Date) {
         margin-bottom: var(--space-lg);
     }
 
-    .back {
-        margin-bottom: var(--space-sm);
-        font-size: 0.85rem;
-    }
-
-    .back a {
-        color: var(--color-text-dim);
-    }
-
-    .back a:hover {
-        color: var(--color-accent);
-    }
-
     .title {
         font-size: 2rem;
         font-weight: 700;
@@ -176,7 +162,7 @@ function formatDate(date: Date) {
     }
 
     .footer {
-        margin-top: var(--space-lg);
+        margin-top: var(--space-xl);
         text-align: center;
     }