Complete tasks 4.1-4.2: Page management service and HTTP endpoints

- Implemented PageService with full CRUD operations
- Added GetPages, CreatePage, UpdatePage, DeletePage, ReorderPages methods
- Cascade deletion of widgets when page is deleted
- Prevention of last page deletion
- Created page HTTP endpoints (GET, POST, PUT, DELETE, reorder)
- HTMX-friendly HTML fragment responses
- Comprehensive unit tests for service and handlers
- Updated dashboard to use PageService and create default pages

docs/task-4.1-implementation.md

@@ -0,0 +1,134 @@
+# Task 4.1 Implementation: PageService with CRUD Operations
+
+## Overview
+Implemented the PageService with all required CRUD operations for managing user pages in the Custom Start Page application.
+
+## Implementation Details
+
+### File: `internal/services/page_service.go`
+
+#### Methods Implemented
+
+1. **GetPages(ctx, userID) ([]*Page, error)**
+   - Queries all pages for a user from DynamoDB
+   - Sorts pages by their order field
+   - Returns pages in display order
+
+2. **CreatePage(ctx, userID, name) (*Page, error)**
+   - Creates a new page with a unique UUID
+   - Automatically assigns the next order number
+   - Sets timestamps (CreatedAt, UpdatedAt)
+   - Persists to DynamoDB Pages table
+
+3. **CreateDefaultPage(ctx, userID) (*Page, error)**
+   - Creates the default "Home" page for new users
+   - Wrapper around CreatePage with "Home" as the name
+   - Satisfies Requirement 2.1
+
+4. **UpdatePage(ctx, userID, pageID, name) (*Page, error)**
+   - Updates a page's name
+   - Updates the UpdatedAt timestamp
+   - Returns the updated page
+   - Uses DynamoDB UpdateItem with ReturnValues
+
+5. **DeletePage(ctx, userID, pageID) error**
+   - Validates that it's not the last page (prevents deletion)
+   - Queries all widgets associated with the page
+   - Cascade deletes all widgets in batches of 25 (DynamoDB limit)
+   - Deletes the page itself
+   - Satisfies Requirements 2.5, 2.6
+
+6. **ReorderPages(ctx, userID, pageOrder) error**
+   - Validates all page IDs exist and belong to the user
+   - Validates the order list length matches existing pages
+   - Updates each page's order field atomically
+   - Updates timestamps
+   - Satisfies Requirement 2.7
+
+#### Helper Functions
+
+- **sortPagesByOrder(pages)**: In-place bubble sort for pages by order field
+
+## Requirements Satisfied
+
+- ✅ **Requirement 2.1**: Default "Home" page creation for new users
+- ✅ **Requirement 2.2**: Page creation with name prompt
+- ✅ **Requirement 2.3**: Page name updates
+- ✅ **Requirement 2.5**: Page deletion with cascade delete of widgets
+- ✅ **Requirement 2.6**: Prevention of last page deletion
+- ✅ **Requirement 2.7**: Page reordering with persistence
+- ✅ **Requirement 2.8**: Immediate persistence to storage
+
+## Testing
+
+### Unit Tests (`internal/services/page_service_test.go`)
+
+Comprehensive test coverage including:
+
+1. **TestCreateDefaultPage**: Verifies default "Home" page creation
+2. **TestGetPages**: Tests retrieving and sorting multiple pages
+3. **TestGetPagesEmptyResult**: Tests empty result handling
+4. **TestCreatePage**: Tests page creation with auto-incrementing order
+5. **TestUpdatePage**: Tests page name updates
+6. **TestDeletePage**: Tests page deletion
+7. **TestDeleteLastPagePrevention**: Validates last page deletion prevention
+8. **TestDeletePageWithWidgets**: Tests cascade deletion of widgets
+9. **TestReorderPages**: Tests page reordering
+10. **TestReorderPagesInvalidLength**: Tests validation of order list length
+11. **TestReorderPagesInvalidPageID**: Tests validation of page IDs
+12. **TestReorderPagesPersistence**: Tests persistence of reordered pages
+
+### Unit Tests Without DynamoDB (`internal/services/page_service_unit_test.go`)
+
+Tests that don't require DynamoDB:
+
+1. **TestSortPagesByOrder**: Tests sorting function
+2. **TestSortPagesByOrderAlreadySorted**: Tests already sorted pages
+3. **TestSortPagesByOrderReversed**: Tests reversed pages
+4. **TestSortPagesByOrderEmpty**: Tests empty slice
+5. **TestSortPagesByOrderSingle**: Tests single page
+
+**Status**: All unit tests pass ✅
+
+## Key Design Decisions
+
+1. **Cascade Deletion**: When a page is deleted, all associated widgets are automatically deleted to maintain data integrity.
+
+2. **Last Page Protection**: The service prevents deletion of the last page to ensure users always have at least one page.
+
+3. **Batch Operations**: Widget deletion uses DynamoDB BatchWriteItem with batches of 25 items to handle pages with many widgets efficiently.
+
+4. **Order Management**: Pages maintain an order field that determines display sequence. The CreatePage method automatically assigns the next available order number.
+
+5. **Validation**: ReorderPages validates that all page IDs exist and belong to the user before making any changes.
+
+6. **Atomic Updates**: Each page update is atomic, ensuring consistency even with concurrent operations.
+
+## Dependencies
+
+- `github.com/aws/aws-sdk-go-v2`: AWS SDK for DynamoDB operations
+- `github.com/google/uuid`: UUID generation for page IDs
+- `github.com/stretchr/testify`: Testing assertions
+
+## Integration Points
+
+- **Storage Layer**: Uses `internal/storage/DynamoDBClient` for all database operations
+- **Models**: Uses `internal/models.Page` and `internal/models.Widget` data structures
+- **Future Integration**: Will be used by HTTP handlers in `internal/handlers` for page management endpoints
+
+## Notes
+
+- Tests require DynamoDB local running on `http://localhost:8000`
+- AWS credentials must be configured (can be dummy credentials for local testing)
+- The service is stateless and thread-safe
+- All operations use context for cancellation and timeout support
+
+## Next Steps
+
+Task 4.2 will implement the HTTP endpoints that use this service:
+- GET /dashboard
+- GET /pages/:id
+- POST /pages
+- PUT /pages/:id
+- DELETE /pages/:id
+- POST /pages/reorder