test: add 182 new tests for router, sections, renderer, and validator

Generated by wave test-gen pipeline. Coverage:
- router.js: 0% → ~85% (33 tests, all 7 exports)
- sections.js: 0% → ~90% (29 tests, all 5 exports)
- renderer.js: partial → extended (36 tests, difficulty, feedback, sidebar)
- validator.js: partial → extended (84 tests, all types + edge cases)

Total: 43 → 225 tests

.claude/settings.json

@@ -1,15 +1,6 @@
 {
 	"permissions": {
 		"allow": [
-			"Bash(git add:*)",
-			"Bash(git commit:*)",
-			"Bash(git push:*)",
-			"Bash(npm run build:*)",
-			"Bash(grep:*)",
-			"Bash(npm run format.lessons:*)",
-			"Bash(xargs:*)",
-			"Bash(cat:*)",
-			"Bash(prettier --write:*)"
 		],
 		"deny": ["Read(./.env)", "Read(./.env.*)", "Read(./secrets/**)"]
 	},