feat: recover portfolio pages from scratch workspaces

- Add base layouts (BaseLayout, BlogLayout, ProjectLayout)
- Add UI components (Header, Footer, Navigation, Card, Tag)
- Add About page with personal story
- Add Projects pages (index, detail)
- Add homepage content
- Add SEO files (robots.txt, webmanifest)

Work was done by agents in isolated workspaces.
Consolidated into main repo for proper git tracking.

src/components/layout/Header.astro

@@ -0,0 +1,14 @@
+---
+import Navigation from './Navigation.astro';
+---
+
+<header class="sticky top-0 z-50 bg-background/80 backdrop-blur-md border-b border-text-tertiary/20">
+  <div class="max-w-6xl mx-auto px-4 sm:px-6 lg:px-8">
+    <div class="flex items-center justify-between h-16">
+      <a href="/" class="text-xl font-bold text-primary hover:text-secondary transition-colors">
+        DA
+      </a>
+      <Navigation />
+    </div>
+  </div>
+</header>