feat: implement dashboard mobile responsiveness v3 overhaul (#80)

This pull request implements **Mobile Responsiveness (v3) and a High-Fidelity Overhaul** for the dashboard view layer (`/dashboard`, `/catalog`, `/my-books`, `/profile`), matching the design aesthetics of the production mobile e-reader layout.

### Key Changes
1. **Re-engineered Floating Navigation Dock Capsule:**
   - Detached bottom capsule, floating 16px off the bottom with rounded `30px` borders.
   - Glassmorphic look in dark mode (`rgba(26, 26, 30, 0.75)`) and sepia theme in light mode (`rgba(244, 241, 234, 0.9)`).
   - Removed `translateY` offset on the central "AI" action button (robot icon inside a solid green circle).
   - Used `::deep` overrides to clean up text colors and icons, preventing browser visited link purple color defaults on `NavLink` items.
   - Restored compact standalone text labels under the navigation icons.
2. **Dashboard Layout Scale Compression & Fold Optimization:**
   - Compressed profile header avatar (`40px`), welcome title font size, and status pill spacing.
   - Compressed the `concepts-linear-stack` height to `120px` with scrolling.
   - Reduced book cover heights inside `MyBooks` to `200px` on mobile viewports.
3. **Current Reading Widget & Layout Margin Safety:**
   - Localized the widget button label to `"Kontynuuj czytanie"`.
   - Used safe area clearances (`calc(1.5rem + 72px + env(safe-area-inset-bottom))`) at the bottom of pages to prevent content from being covered by the capsule.
4. **Resolved Horizontal Layout Width Blowout (Grid Fix):**
   - Discovered that `.secondary-grid` was using flex layout inherited from desktop rather than grid layout on mobile.
   - Nowrap paragraphs in the concept list stretched the flex container to over 12,000 pixels wide, breaking the entire dashboard layout width.
   - Overrode `.secondary-grid` to `display: grid !important` on mobile, properly constraining layout width and allowing nowrap concept text truncation.

### Verification
- All code changes compiled successfully under `dotnet build NexusReader.slnx --no-restore` (0 errors).
- Validated correct layouts in list view, chart view, and light/dark theme toggles on a Samsung Galaxy S20 Ultra (412x915) viewport.

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #80
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

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

@@ -194,7 +194,11 @@
     display: none;
 }
 
-@media (max-width: 768px) {
+.reader-mobile-dock {
+    display: none;
+}
+
+@media (max-width: 767px) {
     .nexus-mobile-topbar {
         display: flex;
         align-items: center;
@@ -262,7 +266,7 @@
         width: 32px;
         height: 32px;
         background: linear-gradient(135deg, var(--nexus-neon) 0%, #0099ff 100%);
-        border: 1px solid rgba(255, 255, 255, 0.1);
+        border: 1px solid var(--border);
         border-radius: 50%;
         display: flex;
         align-items: center;
@@ -388,7 +392,6 @@
     /* User avatar mini: solid accent, white text, no neon glow */
     .theme-light .user-avatar-mini {
         background: #10b981;
-        border: 1px solid rgba(0, 0, 0, 0.08);
         color: #ffffff;
         box-shadow: 0 2px 8px rgba(16, 185, 129, 0.15);
     }
@@ -414,8 +417,144 @@
         box-shadow: 10px 0 30px rgba(139, 130, 115, 0.2);
     }
 
-    /* Mobile topbar: warm paper border */
-    .theme-light .nexus-mobile-topbar {
-        border-bottom-color: rgba(0, 0, 0, 0.08);
+
+    /* Content padding for bottom navigation dock */
+    .hub-content {
+        padding: 1.25rem 1.25rem calc(1.25rem + 96px + env(safe-area-inset-bottom, 0px)) !important;
+    }
+
+    /* Reader Mobile Dock v3 */
+    ::deep .reader-mobile-dock {
+        display: flex;
+        position: fixed;
+        bottom: calc(16px + env(safe-area-inset-bottom, 0px));
+        left: 20px;
+        right: 20px;
+        height: 64px;
+        background: rgba(26, 26, 30, 0.75); /* Translucent dark mode */
+        backdrop-filter: blur(20px);
+        -webkit-backdrop-filter: blur(20px);
+        border: 1px solid var(--border); /* Microscopic perimeter border */
+        border-radius: 30px; /* Floating capsule rounded borders */
+        z-index: 150;
+        padding: 0 16px;
+        justify-content: space-around;
+        align-items: center;
+        box-shadow: 0 8px 32px rgba(0, 0, 0, 0.4);
+    }
+    
+    ::deep .dock-item {
+        display: flex;
+        flex-direction: column;
+        align-items: center;
+        justify-content: center;
+        flex: 1;
+        height: 100%;
+        color: var(--text-muted);
+        text-decoration: none;
+        transition: color 0.2s ease, filter 0.2s ease;
+        position: relative;
+        gap: 2px;
+    }
+    
+    ::deep .dock-item:hover, ::deep .dock-item.active {
+        color: var(--accent) !important;
+        filter: drop-shadow(0 0 4px var(--accent-glow)); /* Clean accent glow drop-shadow */
+    }
+
+    ::deep .dock-item ::deep svg,
+    ::deep .dock-item ::deep .nexus-icon,
+    ::deep .dock-item svg,
+    ::deep .dock-item .nexus-icon {
+        color: inherit !important;
+        fill: currentColor !important;
+    }
+    
+    ::deep .dock-text {
+        display: block !important;
+        font-size: 10px;
+        font-weight: 500;
+        margin-top: 2px;
+        white-space: nowrap;
+        color: inherit;
+    }
+
+    /* Central action button style */
+    ::deep .dock-item.central-action {
+        display: flex;
+        flex-direction: column;
+        align-items: center;
+        justify-content: center;
+        position: relative;
+        flex: 1;
+        height: 100%;
+        gap: 2px;
+        margin-top: 0;
+        transform: none !important;
+        z-index: 160;
+    }
+    
+    ::deep .central-action-inner {
+        width: 36px;
+        height: 36px;
+        border-radius: 50%;
+        background: var(--accent); /* Solid green background */
+        color: #ffffff !important; /* White robot icon */
+        display: flex;
+        align-items: center;
+        justify-content: center;
+        border: none !important;
+        box-shadow: 0 4px 10px rgba(0, 255, 153, 0.3);
+        transition: transform 0.2s cubic-bezier(0.4, 0, 0.2, 1), box-shadow 0.2s ease;
+    }
+
+    ::deep .central-action-inner ::deep svg,
+    ::deep .central-action-inner ::deep .nexus-icon,
+    ::deep .central-action-inner svg,
+    ::deep .central-action-inner .nexus-icon {
+        color: #ffffff !important;
+        fill: currentColor !important;
+    }
+    
+    ::deep .dock-item.central-action:hover .central-action-inner,
+    ::deep .dock-item.central-action.active .central-action-inner {
+        transform: scale(1.05);
+        box-shadow: 0 4px 14px rgba(0, 255, 153, 0.5);
+    }
+
+    ::deep .central-action-glow {
+        display: none; /* Purged background glow */
+    }
+
+    /* Light Theme Overrides */
+    .theme-light ::deep .reader-mobile-dock {
+        background: rgba(244, 241, 234, 0.9); /* Translucent light mode warm paper background */
+        box-shadow: 0 8px 30px rgba(139, 130, 115, 0.15);
+    }
+    
+    .theme-light ::deep .dock-item {
+        color: var(--text-muted);
+    }
+    
+    .theme-light ::deep .dock-item:hover, .theme-light ::deep .dock-item.active {
+        color: var(--accent) !important;
+        filter: drop-shadow(0 0 3px var(--accent-glow));
+    }
+    
+    .theme-light ::deep .central-action-inner {
+        background: var(--accent) !important;
+        color: #ffffff !important;
+        border: none !important;
+        box-shadow: 0 4px 10px rgba(16, 185, 129, 0.25) !important;
+    }
+    
+    .theme-light ::deep .dock-item.central-action:hover .central-action-inner,
+    .theme-light ::deep .dock-item.central-action.active .central-action-inner {
+        box-shadow: 0 4px 14px rgba(16, 185, 129, 0.35) !important;
+        transform: scale(1.05);
+    }
+    
+    .theme-light ::deep .central-action-glow {
+        display: none;
     }
 }