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

packages/shared/src/types/database.types.ts

@@ -183,3 +183,29 @@ export interface KnowledgeEntry extends BaseEntity {
 export interface KnowledgeEntryWithTags extends KnowledgeEntry {
   tags: KnowledgeTag[];
 }
+
+/**
+ * Domain entity
+ */
+export interface Domain extends BaseEntity {
+  workspaceId: string;
+  name: string;
+  slug: string;
+  description: string | null;
+  color: string | null;
+  icon: string | null;
+  sortOrder: number;
+  metadata: Record<string, unknown>;
+}
+
+/**
+ * Domain with usage counts
+ */
+export interface DomainWithCounts extends Domain {
+  _count?: {
+    tasks: number;
+    projects: number;
+    events: number;
+    ideas: number;
+  };
+}