feat(creator): overhaul Creator flow, editor duplication, and staging setup (#83)

This pull request completely overhauls the Creator editor flow, resolves the editor duplication race condition, aligns layout/styling themes in light and dark mode, and adds Docker staging setups.

### Key Changes
1. **Creator Flow Polish**: Redesigned the editor canvas to prevent double scrolling by delegating overflow to the editor canvas layer, updated styles to a premium aesthetic.
2. **Race Condition Prevention**: Resolved Crepe editor duplication when loading or switching chapters by tracking state via shared window maps (`window.editorCache`, `window.editorStates`) and checking `_lastInitializedEditorId` synchronously in Blazor.
3. **Theme Synchronization**: Integrated explicit theme initialization (`ThemeService.InitializeAsync()`) and anchored CSS isolation selectors to correctly sync with Light (Soft Sepia) and Deep Dark theme preferences.
4. **Staging Automation**: Created staging docker configurations with `--nexus-only` flag to allow iterative development without resetting PG/Neo4j database containers.

---------

Co-authored-by: Marek Jasiński <jasins.marek@gmail.com>
Reviewed-on: #83
Co-authored-by: Antigravity <antigravity@google.com>
Co-committed-by: Antigravity <antigravity@google.com>

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

@@ -354,6 +354,8 @@
 /* --- Desktop Sidebar: warm paper shadow --- */
 .theme-light ::deep .hub-sidebar {
     box-shadow: 4px 0 20px rgba(139, 130, 115, 0.08);
+    background: var(--bg-surface) !important;
+    border-right: 1px solid var(--border) !important;
 }
 
 /* --- Logo icon: remove neon glow --- */