✅ test(skilltree): add comprehensive test suite for web and backend

Add 91 tests covering the SkillTree application:

Web (Vitest - 53 tests):
- Level calculation and XP progress functions
- Branch validation and factory functions
- createDefaultSkill and createActivity helpers

Backend (Jest - 38 tests):
- SkillService CRUD operations
- XP system with level-up detection
- User stats aggregation
- Custom Drizzle ORM mock with thenable query builder

apps/skilltree/apps/web/package.json

@@ -9,20 +9,26 @@
 		"prepare": "svelte-kit sync || echo ''",
 		"check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
 		"check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch",
-		"type-check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json"
+		"type-check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
+		"test": "vitest",
+		"test:run": "vitest run",
+		"test:coverage": "vitest run --coverage"
 	},
 	"devDependencies": {
 		"@sveltejs/adapter-node": "^5.0.0",
 		"@sveltejs/kit": "^2.0.0",
 		"@sveltejs/vite-plugin-svelte": "^5.0.0",
 		"@tailwindcss/vite": "^4.1.7",
+		"@testing-library/svelte": "^5.2.6",
 		"@types/node": "^20.0.0",
+		"jsdom": "^25.0.1",
 		"svelte": "^5.0.0",
 		"svelte-check": "^4.0.0",
 		"tailwindcss": "^4.1.7",
 		"tslib": "^2.4.1",
 		"typescript": "^5.0.0",
-		"vite": "^6.0.0"
+		"vite": "^6.0.0",
+		"vitest": "^4.0.18"
 	},
 	"dependencies": {
 		"@manacore/shared-auth": "workspace:*",