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/developer/api/dashboard.md

@@ -0,0 +1,82 @@
+# Dashboard API
+
+## Get Dashboard Sections
+
+Retrieve all dashboard sections for a specific library, including smart sections and user collections.
+
+**Endpoint**: `GET /api/dashboard/sections`
+
+**Authentication**: Required (Bearer token)
+
+### Query Parameters
+
+| Parameter | Type   | Required | Description                                   |
+|-----------|--------|----------|-----------------------------------------------|
+| library_id| string | Yes      | Library UUID to fetch sections for             |
+| limit     | number | No       | Items per section (default: 20, max: 100)      |
+
+### Response
+
+Returns array of sections in user's customized order (respects `section_order` and `hidden_sections` preferences).
+
+**Section Types**:
+- `smart`: Auto-generated sections based on reading activity
+- `collection`: User-created collections with `show_on_dashboard: true`
+
+**Smart Sections**:
+| ID              | Title            | Icon | Description                                      |
+|-----------------|------------------|------|--------------------------------------------------|
+| continue-reading| Continue Reading | 📖   | Books with progress > 0% and < 100%              |
+| in-progress     | In Progress      | 📚   | Books with progress > 0%                         |
+| recently-added  | Recently Added   | 🆕   | Newest items in library                          |
+| recently-read   | Recently Read    | ✅   | Books with progress = 100%                       |
+| unread          | Not Started      | 📕   | Books with no reading progress                   |
+
+### Example Response
+
+```json
+{
+  "sections": [
+    {
+      "id": "continue-reading",
+      "type": "smart",
+      "title": "Continue Reading",
+      "icon": "📖",
+      "items": [
+        {
+          "id": "uuid-here",
+          "title": "Book Title",
+          "author": "Author Name",
+          "cover_image_path": "/path/to/cover.jpg"
+        }
+      ],
+      "view_all_url": "/section/continue-reading"
+    },
+    {
+      "id": "collection-uuid",
+      "type": "collection",
+      "title": "My Favorites",
+      "icon": "⭐",
+      "items": [],
+      "view_all_url": null
+    }
+  ]
+}
+```
+
+### User Preferences
+
+The endpoint respects user's dashboard preferences:
+
+- **`section_order`**: Sections returned in user's custom order
+- **`hidden_sections`**: Hidden sections excluded from response
+- **`items_per_section`**: Default limit from user preferences (overridden by `?limit=` query param)
+
+### Error Responses
+
+| Status | Description            |
+|--------|------------------------|
+| 400    | Missing library_id     |
+| 400    | Invalid library_id     |
+| 401    | Unauthorized           |
+| 500    | Failed to load sections |