feat : add dashboard with Chart.js charts and filters

Implement the dashboard page with real data from the API:
- KPI cards (hours, active tasks, total tasks, projects)
- Charts: hours by day (line), hours by project (doughnut),
  tasks by status (doughnut), tasks by priority (bar),
  tasks by project (horizontal stacked bar)
- Filters: period (week/month), project, user
- Add chart.js and vue-chartjs dependencies
- Add dashboard sidebar icon and translations

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/plugins/chartjs.client.ts

@@ -0,0 +1,28 @@
+import {
+    Chart as ChartJS,
+    Title,
+    Tooltip,
+    Legend,
+    ArcElement,
+    BarElement,
+    LineElement,
+    PointElement,
+    CategoryScale,
+    LinearScale,
+    Filler,
+} from 'chart.js'
+
+export default defineNuxtPlugin(() => {
+    ChartJS.register(
+        Title,
+        Tooltip,
+        Legend,
+        ArcElement,
+        BarElement,
+        LineElement,
+        PointElement,
+        CategoryScale,
+        LinearScale,
+        Filler,
+    )
+})