✨ 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/app/composables/useFetchSkills.ts

@@ -0,0 +1,14 @@
+import type { SkillsResponse } from '~/types/skill'
+
+export function useFetchSkills() {
+  const config = useRuntimeConfig()
+  const { locale } = useI18n()
+
+  return useFetch<SkillsResponse>('/skills', {
+    baseURL: config.public.apiUrl as string,
+    headers: {
+      'X-API-Key': config.public.apiKey as string,
+      'Accept-Language': locale.value,
+    },
+  })
+}