✨ Add skills page with category grouping (Story 2.4)

- Enhance Skill model with getCurrentLevel() and ordered scope
- Update SkillController to group by category with translated labels
- Add level and project_count to SkillResource
- Create skill.ts types (Skill, SkillCategory, SkillsResponse)
- Create useFetchSkills composable
- Create SkillCard component with animated progress bar
- Implement competences.vue with:
  - Responsive grid (2/3/4 columns)
  - Category sections with icons
  - Stagger animations (respects prefers-reduced-motion)
  - Loading/error/empty states
  - Placeholder for vis.js skill tree (Epic 3)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/i18n/fr.json

@@ -94,14 +94,25 @@
     "previous": "Projet pr\u00e9c\u00e9dent",
     "next": "Projet suivant"
   },
+  "skills": {
+    "title": "Mes Comp\u00e9tences",
+    "page_title": "Comp\u00e9tences | Skycel",
+    "page_description": "D\u00e9couvrez les comp\u00e9tences techniques et soft skills de C\u00e9lian, d\u00e9veloppeur web full-stack.",
+    "load_error": "Impossible de charger les comp\u00e9tences...",
+    "no_skills": "Aucune comp\u00e9tence pour le moment",
+    "skill_tree_placeholder": "Arbre de comp\u00e9tences interactif (bient\u00f4t disponible)",
+    "level": "Niveau",
+    "project": "projet",
+    "projects": "projets"
+  },
   "pages": {
     "projects": {
       "title": "Projets",
-      "description": "Découvrez mes projets et réalisations"
+      "description": "D\u00e9couvrez mes projets et r\u00e9alisations"
     },
     "skills": {
-      "title": "Compétences",
-      "description": "Mes compétences techniques et humaines"
+      "title": "Comp\u00e9tences",
+      "description": "Mes comp\u00e9tences techniques et humaines"
     },
     "testimonials": {
       "title": "Témoignages",