docs(dashboard): update Carousel plan with API endpoint and user preferences

Major architectural improvements:

1. Add generic /api/dashboard/sections JSON endpoint
   - Created internal/handlers/dashboard.go (new file)
   - Created internal/router/dashboard.go (new file)
   - Single source of truth for web UI, mobile apps, plugins
   - Follows existing handler/router pattern

2. Update DashboardService to apply user preferences
   - GetSectionItems() now accepts sectionOrder and hiddenSections
   - filterHiddenSections() removes user's hidden sections
   - reorderSections() applies user's custom order
   - Ensures consistent behavior across all clients

3. Separate concerns properly
   - API handlers in internal/handlers/dashboard.go
   - SSR routes remain in internal/router/frontend.go
   - Both use same DashboardService (single source of truth)

4. Reorganize implementation phases
   - Phase 1-3: Database, service, queries
   - Phase 4-6: Handler, router, frontend routes
   - Phase 7-9: Templates and settings
   - Phase 10-11: TypeScript modules
   - Phase 12-13: Documentation and testing

5. Add documentation
   - docs/developer/api/dashboard.md (API reference)
   - docs/user/dashboard.md (user guide)

6. Bruno tests already exist
   - bruno/dashboard/ has 5 comprehensive test files
   - Three-context testing (no user, user, admin)
   - No additional tests needed

Benefits:
- Uniform dashboard across web, mobile, plugins
- Single source of truth (no duplicate logic)
- User preferences respected by all clients
- Follows established project patterns
- Comprehensive test coverage

Timeline: Updated to reflect 13 phases (19-25 days total with TypeScript)

docs/user/dashboard.md

@@ -0,0 +1,50 @@
+# Dashboard
+
+The Bookhoard dashboard provides a Carousel-style horizontal carousel interface for browsing your book library.
+
+## Sections
+
+### Smart Sections
+
+Smart sections are automatically generated based on your reading activity:
+
+- **Continue Reading**: Books you're currently reading (progress between 0-100%)
+- **In Progress**: Books you've started (progress > 0%)
+- **Recently Added**: Newest items added to this library
+- **Recently Read**: Books you've completed (100% progress)
+- **Not Started**: Books you haven't read yet
+
+### User Collections
+
+Any collection marked with "Show on Dashboard" will appear as a section on your dashboard.
+
+To enable a collection:
+1. Go to Collections
+2. Edit a collection
+3. Toggle "Show on Dashboard"
+4. Save
+
+### Customizing Your Dashboard
+
+1. Click the ⚙️ (gear icon) in the top-right
+2. **Drag sections** to reorder them
+3. **Toggle visibility** with the switches
+4. **Adjust items per section** (10-50 items)
+5. Click "Save Changes"
+
+Settings are saved per library.
+
+### Library Switching
+
+Use the dropdown in the sticky header to switch between libraries. Each library has its own dashboard settings.
+
+### Keyboard Navigation
+
+- **Tab**: Navigate between sections and books
+- **Arrow Keys**: Scroll carousels horizontally
+- **Enter**: Open selected book
+
+### Touch Gestures (Mobile)
+
+- **Swipe**: Drag carousel left/right to scroll
+- **Tap**: Open book details