✨ 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/en.json

@@ -94,6 +94,17 @@
     "previous": "Previous project",
     "next": "Next project"
   },
+  "skills": {
+    "title": "My Skills",
+    "page_title": "Skills | Skycel",
+    "page_description": "Discover the technical skills and soft skills of C\u00e9lian, full-stack web developer.",
+    "load_error": "Unable to load skills...",
+    "no_skills": "No skills yet",
+    "skill_tree_placeholder": "Interactive skill tree (coming soon)",
+    "level": "Level",
+    "project": "project",
+    "projects": "projects"
+  },
   "pages": {
     "projects": {
       "title": "Projects",