refactor(notes): extract title validation into domain service

src/lib/noteValidation.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from 'vitest'
+import { isTitleValid, normalizeTitle } from './noteValidation'
+
+describe('isTitleValid', () => {
+  it('accepts a non-empty title', () => {
+    expect(isTitleValid('Courses')).toBe(true)
+  })
+
+  it('rejects an empty title', () => {
+    expect(isTitleValid('')).toBe(false)
+  })
+
+  it('rejects a whitespace-only title', () => {
+    expect(isTitleValid('   ')).toBe(false)
+  })
+})
+
+describe('normalizeTitle', () => {
+  it('trims surrounding whitespace', () => {
+    expect(normalizeTitle('  Courses  ')).toBe('Courses')
+  })
+
+  it('keeps an already trimmed title unchanged', () => {
+    expect(normalizeTitle('Courses')).toBe('Courses')
+  })
+})