feat(intent): IntentService for set/dismiss with validation

Task 20 of the slice plan. Thin wrapper over the repo's intent
methods that adds two preconditions: setIntent rejects empty
trimmed text, both methods throw "note not found" when the
note id doesn't exist. Repo-level COALESCE on
intent_prompted_at preserves the first-prompt invariant
(spec §3.3); IntentService's job is just input guarding so
the IPC handler stays a one-liner.

Verification: `npx vitest run tests/unit/IntentService.test.ts`
4 passed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/main/services/IntentService.ts

@@ -0,0 +1,16 @@
+import type { NoteRepository } from '../repository/NoteRepository.js';
+
+export class IntentService {
+  constructor(private repo: NoteRepository) {}
+
+  setIntent(noteId: string, text: string): void {
+    if (text.trim().length === 0) throw new Error('empty intent text');
+    if (!this.repo.findById(noteId)) throw new Error('note not found');
+    this.repo.setIntent(noteId, text);
+  }
+
+  dismissIntent(noteId: string): void {
+    if (!this.repo.findById(noteId)) throw new Error('note not found');
+    this.repo.dismissIntent(noteId);
+  }
+}

tests/unit/IntentService.test.ts

@@ -0,0 +1,42 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import Database from 'better-sqlite3';
+import { runMigrations } from '@main/db/migrations/index.js';
+import { NoteRepository } from '@main/repository/NoteRepository.js';
+import { IntentService } from '@main/services/IntentService.js';
+
+describe('IntentService', () => {
+  let db: Database.Database;
+  let repo: NoteRepository;
+  let svc: IntentService;
+
+  beforeEach(() => {
+    db = new Database(':memory:');
+    runMigrations(db);
+    repo = new NoteRepository(db);
+    svc = new IntentService(repo);
+  });
+
+  it('setIntent stores text on note', () => {
+    const { id } = repo.create({ rawText: 'x' });
+    svc.setIntent(id, '내일의 나에게');
+    expect(repo.findById(id)?.userIntent).toBe('내일의 나에게');
+  });
+
+  it('dismissIntent stamps prompted_at without setting intent', () => {
+    const { id } = repo.create({ rawText: 'x' });
+    svc.dismissIntent(id);
+    const note = repo.findById(id)!;
+    expect(note.userIntent).toBeNull();
+    expect(note.intentPromptedAt).not.toBeNull();
+  });
+
+  it('rejects empty intent text', () => {
+    const { id } = repo.create({ rawText: 'x' });
+    expect(() => svc.setIntent(id, '   ')).toThrow(/empty/i);
+  });
+
+  it('throws if note does not exist', () => {
+    expect(() => svc.setIntent('nonexistent', 'x')).toThrow(/not found/i);
+    expect(() => svc.dismissIntent('nonexistent')).toThrow(/not found/i);
+  });
+});