Update dashboard navigation and dynamic loading

- Changed NavMenu to link to /dashboards instead of /dashboards/default
- Refactored Dashboard.razor to list dashboards from API
- Dashboard viewer/designer now loads by selected dashboard ID
- Mode toggle preserves selected dashboard and mode
- Added DashboardApiClient and DashboardInfoDto for API integration
- Registered DashboardApiClient for DI and HTTP client setup in Program.cs

DbFirst.BlazorWasm/Layout/NavMenu.razor

@@ -22,7 +22,7 @@
             </NavLink>
         </div>
         <div class="nav-item px-3">
-            <NavLink class="nav-link" href="dashboards/default">
+            <NavLink class="nav-link" href="dashboards">
                 <span class="oi oi-list-rich" aria-hidden="true"></span> Dashboards
             </NavLink>
         </div>