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/projects/projects.service.spec.ts

@@ -3,6 +3,7 @@ import { Test, TestingModule } from "@nestjs/testing";
 import { ProjectsService } from "./projects.service";
 import { PrismaService } from "../prisma/prisma.service";
 import { ActivityService } from "../activity/activity.service";
+import { WebSocketGateway } from "../websocket/websocket.gateway";
 import { ProjectStatus, Prisma } from "@prisma/client";
 import { NotFoundException } from "@nestjs/common";
 
@@ -10,6 +11,7 @@ describe("ProjectsService", () => {
   let service: ProjectsService;
   let prisma: PrismaService;
   let activityService: ActivityService;
+  let wsGateway: WebSocketGateway;
 
   const mockPrismaService = {
     project: {
@@ -28,6 +30,10 @@ describe("ProjectsService", () => {
     logProjectDeleted: vi.fn(),
   };
 
+  const mockWebSocketGateway = {
+    emitProjectUpdated: vi.fn(),
+  };
+
   const mockWorkspaceId = "550e8400-e29b-41d4-a716-446655440001";
   const mockUserId = "550e8400-e29b-41d4-a716-446655440002";
   const mockProjectId = "550e8400-e29b-41d4-a716-446655440003";
@@ -59,12 +65,17 @@ describe("ProjectsService", () => {
           provide: ActivityService,
           useValue: mockActivityService,
         },
+        {
+          provide: WebSocketGateway,
+          useValue: mockWebSocketGateway,
+        },
       ],
     }).compile();
 
     service = module.get<ProjectsService>(ProjectsService);
     prisma = module.get<PrismaService>(PrismaService);
     activityService = module.get<ActivityService>(ActivityService);
+    wsGateway = module.get<WebSocketGateway>(WebSocketGateway);
 
     vi.clearAllMocks();
   });