feat(#15): implement Gantt chart component

- Create GanttChart component with timeline visualization
- Add task bars with status-based color coding
- Implement PDA-friendly language (Target passed vs OVERDUE)
- Support task click interactions
- Comprehensive test coverage (96.18%)
- 33 tests passing (22 component + 11 helper tests)
- Fully accessible with ARIA labels and keyboard navigation
- Demo page at /demo/gantt
- Responsive design with customizable height

Technical details:
- Uses Next.js 16 + React 19 + TypeScript
- Strict typing (NO any types)
- Helper functions to convert Task to GanttTask
- Timeline calculation with automatic range detection
- Status indicators: completed, in-progress, paused, not-started

Refs #15

apps/api/src/websocket/websocket.module.ts

@@ -0,0 +1,11 @@
+import { Module } from '@nestjs/common';
+import { WebSocketGateway } from './websocket.gateway';
+
+/**
+ * WebSocket module for real-time updates
+ */
+@Module({
+  providers: [WebSocketGateway],
+  exports: [WebSocketGateway],
+})
+export class WebSocketModule {}