refactor: rule of coverage are in one place

lib/types.ts

@@ -19,13 +19,15 @@ export const SKILL_LEVEL_VALUES: Record<Exclude<SkillLevel, null>, number> = {
   expert: 3,
 };
 
+export type SkillImportance = "incontournable" | "majeure" | "standard";
+
 export interface Skill {
   id: string;
   name: string;
   description: string;
   icon?: string;
   links: string[];
-  importance?: string;
+  importance: SkillImportance;
 }
 
 export interface SkillCategory {