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/package.json

@@ -16,10 +16,12 @@
         "@nuxtjs/i18n": "^10.2.3",
         "@nuxtjs/tailwindcss": "^6.14.0",
         "@pinia/nuxt": "^0.11.3",
+        "chart.js": "^4.5.1",
         "nuxt": "^4.3.1",
         "nuxt-toast": "^1.4.0",
         "pinia": "^3.0.4",
         "vue": "^3.5.29",
+        "vue-chartjs": "^5.3.3",
         "vue-router": "^4.6.4"
     }
 }