feat(v031): buildVisionPrompt + GenerateInput.images + GenerateOptions.visionModel

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/unit/visionPrompt.test.ts

@@ -0,0 +1,23 @@
+import { describe, it, expect } from 'vitest';
+import { buildVisionPrompt } from '@main/ai/visionPrompt.js';
+
+describe('buildVisionPrompt', () => {
+  it('includes text, todayKst, dueCandidates, and vocab slice when present', () => {
+    const result = buildVisionPrompt(
+      '회의 메모',
+      '2026-05-09',
+      ['2026-05-10', '2026-05-15'],
+      ['work', 'meeting', 'project', 'todo']
+    );
+    expect(result).toContain('회의 메모');
+    expect(result).toContain('2026-05-09');
+    expect(result).toContain('2026-05-10, 2026-05-15');
+    expect(result).toContain('work, meeting, project, todo');
+  });
+
+  it('uses (이미지만 있음) placeholder when text is empty', () => {
+    const result = buildVisionPrompt('', '2026-05-09', [], []);
+    expect(result).toContain('(이미지만 있음)');
+    expect(result).not.toContain('\n\n\n'); // no double-blank from empty text
+  });
+});