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/web/src/lib/api/domains.ts

@@ -0,0 +1,97 @@
+/**
+ * Domain API Client
+ * Handles domain-related API requests
+ */
+
+import type { Domain, DomainWithCounts } from "@mosaic/shared";
+import { apiGet, apiPost, apiPatch, apiDelete, type ApiResponse } from "./client";
+
+/**
+ * Create domain DTO
+ */
+export interface CreateDomainDto {
+  name: string;
+  slug: string;
+  description?: string;
+  color?: string;
+  icon?: string;
+  sortOrder?: number;
+  metadata?: Record<string, unknown>;
+}
+
+/**
+ * Update domain DTO
+ */
+export interface UpdateDomainDto {
+  name?: string;
+  slug?: string;
+  description?: string;
+  color?: string;
+  icon?: string;
+  sortOrder?: number;
+  metadata?: Record<string, unknown>;
+}
+
+/**
+ * Domain filters for querying
+ */
+export interface DomainFilters {
+  search?: string;
+  page?: number;
+  limit?: number;
+}
+
+/**
+ * Fetch all domains
+ */
+export async function fetchDomains(
+  filters?: DomainFilters
+): Promise<ApiResponse<Domain[]>> {
+  const params = new URLSearchParams();
+
+  if (filters?.search) {
+    params.append("search", filters.search);
+  }
+  if (filters?.page) {
+    params.append("page", filters.page.toString());
+  }
+  if (filters?.limit) {
+    params.append("limit", filters.limit.toString());
+  }
+
+  const queryString = params.toString();
+  const endpoint = queryString ? `/api/domains?${queryString}` : "/api/domains";
+
+  return apiGet<ApiResponse<Domain[]>>(endpoint);
+}
+
+/**
+ * Fetch a single domain by ID
+ */
+export async function fetchDomain(id: string): Promise<DomainWithCounts> {
+  return apiGet<DomainWithCounts>(`/api/domains/${id}`);
+}
+
+/**
+ * Create a new domain
+ */
+export async function createDomain(data: CreateDomainDto): Promise<Domain> {
+  return apiPost<Domain>("/api/domains", data);
+}
+
+/**
+ * Update a domain
+ */
+export async function updateDomain(
+  id: string,
+  data: UpdateDomainDto
+): Promise<Domain> {
+  return apiPatch<Domain>(`/api/domains/${id}`, data);
+}
+
+/**
+ * Delete a domain
+ */
+export async function deleteDomain(id: string): Promise<void> {
+  return apiDelete<void>(`/api/domains/${id}`);
+}