feat: Convert website from static HTML to .NET 9.0 Blazor Web App

Major architectural upgrade from static HTML site to modern Blazor Web App:

- Migrated to .NET 9.0 Blazor Web App framework
- Converted home page with 4 gateway cards (Help Desk, App Store, Cloud, SDK)
- Added new SDK card linking to comprehensive SDK documentation
- Converted SDK documentation page to Blazor component
- Updated template download links to nuget.silverlabs.uk repository
- Implemented multi-stage Docker build with .NET SDK 9.0
- Created Blazor-optimized nginx configuration
- Preserved all original styling and animations
- Added .gitignore for Blazor build artifacts

Technical changes:
- New BlazorApp/ project structure with Components architecture
- MainLayout simplified (no default navigation)
- CSS ported to wwwroot (styles.css + sdk-styles.css)
- Multi-stage Dockerfile: Build with dotnet SDK, serve with nginx
- GitLab CI/CD pipeline compatible (auto-detects new Dockerfile)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

BlazorApp/Components/Layout/NavMenu.razor

@@ -0,0 +1,30 @@
+<div class="top-row ps-3 navbar navbar-dark">
+    <div class="container-fluid">
+        <a class="navbar-brand" href="">SilverLabs.Website</a>
+    </div>
+</div>
+
+<input type="checkbox" title="Navigation menu" class="navbar-toggler" />
+
+<div class="nav-scrollable" onclick="document.querySelector('.navbar-toggler').click()">
+    <nav class="nav flex-column">
+        <div class="nav-item px-3">
+            <NavLink class="nav-link" href="" Match="NavLinkMatch.All">
+                <span class="bi bi-house-door-fill-nav-menu" aria-hidden="true"></span> Home
+            </NavLink>
+        </div>
+
+        <div class="nav-item px-3">
+            <NavLink class="nav-link" href="counter">
+                <span class="bi bi-plus-square-fill-nav-menu" aria-hidden="true"></span> Counter
+            </NavLink>
+        </div>
+
+        <div class="nav-item px-3">
+            <NavLink class="nav-link" href="weather">
+                <span class="bi bi-list-nested-nav-menu" aria-hidden="true"></span> Weather
+            </NavLink>
+        </div>
+    </nav>
+</div>
+