feat: Display runtime connection string in dashboard

Added connection string display to System Information section of dashboard.

- Injected IConfiguration into DashboardController
- Added ConnectionString to ViewData
- Displayed in monospace code format for easy reading
- Shows actual runtime connection string from configuration
- Helps verify which database file is being used in different environments

This makes it easier to troubleshoot database location issues, especially
when deploying to different environments (Development, Production, CT109, etc.).

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

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

LittleShop/Areas/Admin/Views/Dashboard/Index.cshtml

@@ -228,6 +228,7 @@ else
                 <ul class="list-unstyled">
                     <li><strong>Framework:</strong> .NET 9.0</li>
                     <li><strong>Database:</strong> SQLite</li>
+                    <li><strong>Connection String:</strong> <code class="text-muted small">@ViewData["ConnectionString"]</code></li>
                     <li><strong>Authentication:</strong> Cookie-based</li>
                     <li><strong>Crypto Support:</strong> 8 currencies via BTCPay Server</li>
                     <li><strong>API Endpoints:</strong> Available for client integration</li>