feat(ui): Hub Navigation, Profile Dashboard and Auth Stability Fixes (#31)

This PR implements the Hub Navigation system and the Profile Dashboard, while resolving critical session synchronization issues.

### Key Changes
- **Hub Navigation**: Introduced `MainHubLayout` with a premium glassmorphism sidebar, providing access to Dashboard, Library, Concepts Map, and Profile.
- **Profile Dashboard**: Implemented a high-fidelity Profile page (#27) with learning metrics, AI token usage tracking, and system rank visualization.
- **Stability Fixes**:
    - Resolved an infinite network loop on the `/profile` page by implementing request deduplication and in-memory caching in `IdentityService`.
    - Added environment-aware guards to prevent illegal JavaScript interop calls during server-side prerendering.
    - Implemented automatic session invalidation on `401 Unauthorized` responses to handle stale authentication states gracefully.
- **Reader Integration**: Added a "Return to Dashboard" option in the reader toolbar (#26).

Closes #26
Closes #27

Reviewed-on: #31
Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Co-committed-by: Marek Jasiński <jasins.marek@gmail.com>

src/NexusReader.UI.Shared/Layout/ReaderLayout.razor.css

@@ -0,0 +1,155 @@
+.app-container {
+    display: grid;
+    grid-template-columns: 1fr auto var(--sidebar-width, 450px);
+    width: 100vw;
+    height: 100vh;
+    overflow: hidden;
+    background: #121212;
+}
+
+
+.reader-pane {
+    background: #F9F9F9;
+    position: relative;
+    overflow: hidden;
+    display: flex;
+    flex-direction: column;
+    z-index: 5;
+    height: 100vh;
+}
+
+main {
+    flex: 1;
+    overflow: hidden;
+    position: relative;
+    display: flex;
+    flex-direction: column;
+}
+
+.intelligence-sidebar {
+    display: grid;
+    grid-template-columns: 50px 1fr;
+    width: 100%; /* controlled by grid */
+    height: 100%;
+    background: #0d0d0d;
+    box-shadow: -10px 0 30px rgba(0, 0, 0, 0.3);
+    border-left: 1px solid rgba(255, 255, 255, 0.1);
+    overflow: hidden;
+    z-index: 10;
+}
+
+.resizer {
+    width: 4px;
+    cursor: col-resize;
+    background: rgba(255, 255, 255, 0.02);
+    transition: background 0.2s, width 0.2s;
+    z-index: 20;
+    border-left: 1px solid rgba(255, 255, 255, 0.05);
+}
+
+.resizer:hover, .app-container.is-resizing .resizer {
+    background: var(--nexus-neon);
+    width: 6px;
+    box-shadow: 0 0 10px var(--nexus-neon);
+}
+
+.app-container.is-resizing {
+    user-select: none;
+}
+
+
+.app-container.focus-mode-active {
+    grid-template-columns: 1fr 0px 50px;
+}
+
+.app-container.focus-mode-active .intelligence-sidebar {
+    grid-template-columns: 50px 0px;
+}
+
+.app-container.focus-mode-active .resizer {
+    display: none;
+}
+
+.app-container.focus-mode-active .intelligence-content {
+    opacity: 0;
+    pointer-events: none;
+}
+
+
+
+.intelligence-content {
+    display: flex;
+    flex-direction: column;
+    height: 100%;
+    overflow: hidden;
+}
+
+.intelligence-header {
+    height: 50px;
+    display: flex;
+    align-items: center;
+    padding: 0 1.5rem;
+    gap: 0.8rem;
+    background: rgba(255, 255, 255, 0.02);
+    border-bottom: 1px solid rgba(255, 255, 255, 0.05);
+    font-family: var(--nexus-font-sans);
+    font-size: 0.9rem;
+    color: #fff;
+    flex-shrink: 0;
+}
+
+.intelligence-header .close-btn {
+    margin-left: auto;
+    background: none;
+    border: none;
+    color: #666;
+    font-size: 1.5rem;
+    cursor: pointer;
+}
+
+.intelligence-scroll-area {
+    flex: 1;
+    overflow-y: auto;
+    display: flex;
+    flex-direction: column;
+}
+
+/* Platform Specifics */
+.platform-mobile .intelligence-sidebar {
+    position: fixed;
+    right: 0;
+    top: 0;
+    bottom: 0;
+    width: 80%;
+    z-index: 100;
+}
+
+#blazor-error-ui {
+    background: lightyellow;
+    bottom: 0;
+    box-shadow: 0 -1px 2px rgba(0, 0, 0, 0.2);
+    display: none;
+    left: 0;
+    padding: 0.6rem 1.25rem 0.7rem 1.25rem;
+    position: fixed;
+    width: 100%;
+    z-index: 1000;
+}
+
+#blazor-error-ui .dismiss {
+    cursor: pointer;
+    position: absolute;
+    right: 0.75rem;
+    top: 0.5rem;
+}
+
+.quiz-available {
+    animation: quiz-pulse 1.5s infinite;
+    color: var(--nexus-neon) !important;
+}
+
+@keyframes quiz-pulse {
+    0% { filter: drop-shadow(0 0 2px var(--nexus-neon)); transform: scale(1); }
+    50% { filter: drop-shadow(0 0 10px var(--nexus-neon)); transform: scale(1.1); }
+    100% { filter: drop-shadow(0 0 2px var(--nexus-neon)); transform: scale(1); }
+}