feat: Sheets 템플릿 가이드 보강(TDD)

- Code.gs에 @tool/@version 헤더, 필드 매핑 TODO, try/catch 에러 처리 추가
- README.txt에 Web App 배포/필드 매핑 가이드 추가
- 테스트 추가: sheets.template.enhance.test.ts
- 전체 테스트 그린 유지

lib/exporter/sheets.template.enhance.test.ts

@@ -0,0 +1,46 @@
+import { describe, it, expect } from 'vitest'
+import { buildExtrasForPage } from '@/lib/exporter/extras'
+import type { Page } from '@/lib/schema/page'
+
+function td(b: Uint8Array){ return new TextDecoder().decode(b) }
+
+const basePage: Page = {
+  title: 'Test',
+  seo: { title: 'T', description: 'D' },
+  theme: { primaryColor: '#0ea5e9', fontFamily: 'Inter' },
+  analytics: { ga4MeasurementId: '', metaPixelId: '', customHeadHtml: '' },
+  sections: [],
+  form: {
+    fields: [],
+    actionUrl: '',
+    spamProtection: { honeypotFieldName: '_hp', minSubmitSeconds: 2 },
+  },
+  locale: 'en',
+}
+
+describe('Sheets template enhance', () => {
+  it('includes version/meta and mapping/error guide in Code.gs and README', () => {
+    const extras = buildExtrasForPage(basePage, { sheetsMode: 'include' })
+    const code = td(extras['sheets/Code.gs'])
+    const readme = td(extras['sheets/README.txt'])
+
+    // version/meta header
+    expect(code).toMatch(/@version:\s*\d+\.\d+\.\d+/)
+    expect(code).toMatch(/@tool:\s*landing-builder/i)
+
+    // field mapping and error handling guides
+    expect(code).toMatch(/TODO:\s*map incoming fields to sheet columns/i)
+    expect(code).toMatch(/try\s*\{/)
+    expect(code).toMatch(/catch\s*\(e\)/)
+
+    // README includes setup and mapping hint
+    expect(readme).toMatch(/Apps Script/i)
+    expect(readme).toMatch(/Deploy as Web App/i)
+    expect(readme).toMatch(/Map fields to columns/i)
+  })
+
+  it('respects exclude mode', () => {
+    const extras = buildExtrasForPage(basePage, { sheetsMode: 'exclude' })
+    expect(Object.keys(extras).some(k => k.startsWith('sheets/'))).toBe(false)
+  })
+})