fix(tag-vocab): T2 review minor/nit 2건 (#3 v0.2.3)

- M1: prompt.test.ts test 4 변수명 candidateIdx → headerIdx (실제 anchor 가 'Today's date' 헤더)
- N1: prompt.ts return 직전 self-delimited block 컨벤션 1줄 코멘트

skip: N2 (PROMPT_VERSION 테스트 redundancy nit — harmless guard), N3 (vocab dedup/normalize — Task 1 caller 책임)

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

src/main/ai/prompt.ts

@@ -17,6 +17,7 @@ ${candidates.map((c, i) => `  ${i + 1}. ${c.iso ?? '(ambiguous)'} — matched to
     ? `\nExisting vocabulary tags (most-used first): ${vocab.join(', ')}\nPrefer reusing a vocabulary tag when the meaning matches; create new tags only when the meaning is genuinely new.\n`
     : '';
 
+  // candidateBlock & vocabBlock are self-delimited with leading/trailing \n
   return `You organize raw personal notes into structured metadata.
 
 Today's date in Korea Standard Time (KST): ${todayKst}

tests/unit/prompt.test.ts

@@ -19,13 +19,13 @@ describe('prompt', () => {
     expect(out).toContain('Prefer reusing');
   });
 
-  it('vocab block appears between candidate block and JSON rules', () => {
+  it('vocab block appears after header and before JSON rules', () => {
     const out = buildPrompt('hello', '2026-05-02', [], ['design']);
-    const candidateIdx = out.indexOf("Today's date");
+    const headerIdx = out.indexOf("Today's date");
     const vocabIdx = out.indexOf('Existing vocabulary');
     const jsonRulesIdx = out.indexOf('Return a JSON object');
-    expect(candidateIdx).toBeGreaterThan(-1);
-    expect(vocabIdx).toBeGreaterThan(candidateIdx);
+    expect(headerIdx).toBeGreaterThan(-1);
+    expect(vocabIdx).toBeGreaterThan(headerIdx);
     expect(jsonRulesIdx).toBeGreaterThan(vocabIdx);
   });
 });