feat: add Browse page with paginated publication index

Add a /browse page showing all publications with client-side pagination,
sorting, and card-based layout. Add Browse nav link to header. Convert
homepage Browse Articles button from search dialog trigger to /browse link.

Author: hubsmoke

src/components/Header.astro

@@ -23,6 +23,10 @@ import SearchDialog from './SearchDialog.astro';
       <wa-icon label="Search" name="magnifying-glass" variant="solid" class="nav-icon brand-text"></wa-icon>
       <span class="brand-text">Search</span>
     </button>
+    <a href="/browse" class="nav-link">
+      <wa-icon label="Browse" name="book-open" variant="solid" class="nav-icon brand-text"></wa-icon>
+      <span class="brand-text">Browse</span>
+    </a>
     <a href="/about" class="nav-link">
       <wa-icon label="About" name="circle-info" variant="solid" class="nav-icon brand-text"></wa-icon>
       <span class="brand-text">About</span>