ux: eliminate white-flash on Blazor navigation from Inquiry page

- App.razor: loading overlay starts with `show` class (visible on cold load)
- admin-session.js: add showLoading()/hideLoading(); MutationObserver detects
  .admin-page-hero / .admin-login-page instead of mud-element count threshold;
  observer restarts on every navigation cycle via LocationChanged
- MainLayout.razor: subscribe to NavigationManager.LocationChanged →
  call JS showLoading() on every route change; implements IDisposable
- InquiryList.razor: remove unused IInquiryRepository injection; load data
  once (GetPagedAsync(1,200)) and pass IReadOnlyList to all six tab panels
- InquiryTable.razor: accept Inquiries parameter; filter synchronously in
  OnParametersSet() — eliminates 6 redundant API calls per page visit
- admin.css: overlay fade-in animation (0.15s); page content fade-in on
  route mount via .admin-page-hero / .admin-login-page animation (0.25s)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

TaxBaik.Web/wwwroot/js/admin-session.js

@@ -4,6 +4,7 @@ window.taxbaikAdminSession = {
             'admin-login-route',
             window.location.pathname.toLowerCase().endsWith('/admin/login'));
     },
+
     clearAuthToken: function () {
         try {
             localStorage.removeItem('auth_token');
@@ -11,54 +12,73 @@ window.taxbaikAdminSession = {
             // Ignore storage errors; redirect still recovers the session.
         }
     },
+
+    showLoading: function () {
+        const overlay = document.getElementById('blazor-loading');
+        if (!overlay) return;
+
+        // Start observer FIRST so it catches the mutation that brings new content in.
+        if (window._taxbaikLoadingObserver) {
+            window._taxbaikLoadingObserver.disconnect();
+        }
+        window._taxbaikLoadingObserver = new MutationObserver(function () {
+            const pageReady =
+                document.querySelector('.admin-page-hero') !== null ||
+                document.querySelector('.admin-login-page') !== null;
+            if (pageReady) {
+                window.taxbaikAdminSession.hideLoading();
+            }
+        });
+        window._taxbaikLoadingObserver.observe(document.body, {
+            childList: true,
+            subtree: true
+        });
+
+        // Show overlay after observer is active.
+        overlay.classList.add('show');
+
+        // Safety fallback: hide after 3 seconds regardless.
+        if (window._taxbaikLoadingTimeout) {
+            clearTimeout(window._taxbaikLoadingTimeout);
+        }
+        window._taxbaikLoadingTimeout = setTimeout(function () {
+            window.taxbaikAdminSession.hideLoading();
+        }, 3000);
+    },
+
+    hideLoading: function () {
+        const overlay = document.getElementById('blazor-loading');
+        if (overlay) {
+            overlay.classList.remove('show');
+        }
+
+        if (window._taxbaikLoadingTimeout) {
+            clearTimeout(window._taxbaikLoadingTimeout);
+            window._taxbaikLoadingTimeout = null;
+        }
+
+        if (window._taxbaikLoadingObserver) {
+            window._taxbaikLoadingObserver.disconnect();
+            window._taxbaikLoadingObserver = null;
+        }
+    },
+
     watchReconnect: function () {
         window.taxbaikAdminSession.syncRouteClass();
         window.addEventListener('popstate', window.taxbaikAdminSession.syncRouteClass);
 
-        // Hide loading indicator after Blazor initializes
-        const loadingOverlay = document.getElementById('blazor-loading');
-        if (loadingOverlay) {
-            const hideLoading = () => {
-                if (loadingOverlay.classList.contains('show')) {
-                    loadingOverlay.classList.remove('show');
-                }
-            };
-
-            // Method 1: Hide after 3 seconds (guaranteed timeout)
-            setTimeout(hideLoading, 3000);
-
-            // Method 2: Hide when Blazor components appear (faster if available)
-            const observer = new MutationObserver(() => {
-                const mudElements = document.querySelectorAll('[class*="mud-"]').length;
-                if (mudElements > 10) {
-                    hideLoading();
-                    observer.disconnect();
-                }
-            });
-            observer.observe(document.body, {
-                childList: true,
-                subtree: true,
-                attributes: true
-            });
-
-            // Method 3: Hide when page is interactive
-            document.addEventListener('readystatechange', () => {
-                if (document.readyState === 'interactive' || document.readyState === 'complete') {
-                    setTimeout(hideLoading, 500);
-                }
-            });
-        }
+        // Show loading on initial page load — overlay has 'show' from HTML,
+        // but we still need to set up the observer to detect when to hide it.
+        window.taxbaikAdminSession.showLoading();
 
         const modal = document.getElementById('components-reconnect-modal');
-        if (!modal) {
-            return;
-        }
+        if (!modal) return;
 
-        const reloadOnRejectedCircuit = () => {
+        const reloadOnRejectedCircuit = function () {
             const className = modal.className || '';
             if (className.includes('components-reconnect-failed') ||
                 className.includes('components-reconnect-rejected')) {
-                window.setTimeout(() => window.location.reload(), 1500);
+                window.setTimeout(function () { window.location.reload(); }, 1500);
             }
         };