feat(editor): align selection popup and all editor control elements styling with Reader (#81)

## Summary of Changes
This pull request aligns all major interactive editor control elements in the Milkdown Crepe editor with the premium `SelectionAiPanel` / `IntelligenceToolbar` glassmorphism design.

### Changes:
1. **Selection Bubble Menu Unification:** Relocated the selection menu overrides from `Creator.razor.css` to `app.css` to resolve scoping bugs. Themed to match the Reader's selection popup 1:1.
2. **Editor Controls Theming:** Themed table cell drag handles, table actions popups, line insertion handles & add buttons, Notion-style paragraph drag handles, and slash commands menus with glassmorphic backgrounds, perimeter borders, hover transitions, and active accent states.
3. **Visibility Lifecycle Fixes:** Excluded `.cell-handle` and `.milkdown-block-handle` from explicit `display: none !important` rules when hidden, preserving their dimensions for correct JS positioning calculations and preventing handles from jumping/sliding.
4. **Table Margin Clipping Fix:** Set `overflow: visible !important` on `.tableWrapper` to allow table controls to draw cleanly into the editor canvas's padding zone without boundary clipping.

Resolves #82.

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #81
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

src/NexusReader.Infrastructure/DependencyInjection.cs

@@ -78,6 +78,7 @@ public static class DependencyInjection
         services.Configure<AiSettings>(configuration.GetSection(AiSettings.SectionName));
         services.Configure<StripeSettings>(configuration.GetSection(StripeSettings.SectionName));
         services.Configure<RagMonetizationOptions>(configuration.GetSection(RagMonetizationOptions.SectionName));
+        services.Configure<HtmlSanitizerSettings>(configuration.GetSection(HtmlSanitizerSettings.SectionName));
         var aiSettings = configuration.GetSection(AiSettings.SectionName).Get<AiSettings>() ?? new AiSettings();
 
         if (string.IsNullOrWhiteSpace(aiSettings.ApiKey) || aiSettings.ApiKey == "PLACEHOLDER")
@@ -124,6 +125,8 @@ public static class DependencyInjection
         // Fix #4: Scoped instead of Singleton — BookStorageService uses path resolution
         // that is environment-specific and incompatible with Singleton lifetime in MAUI.
         services.AddScoped<IBookStorageService, BookStorageService>();
+        services.AddScoped<IStorageService, LocalStorageService>();
+        services.AddSingleton<ISanitizerService, HtmlSanitizerService>();
 
         // Fix #1: Ebook repository (scoped, matches AppDbContext lifetime)
         services.AddScoped<IEbookRepository, EbookRepository>();