make app name and purpose machine-readable on the landing page

Google OAuth branding review rejected the app twice with "no description of
the app purpose on the homepage" and "app name does not match the homepage",
even though both were present in Korean. Two likely causes, both addressed:

- The h1 wrapped an alt="" logo image before the text, so the app name could
  not be extracted from it. The image now sits outside the h1, leaving the
  heading as plain text.
- The page was Korean-only. The app name is now "해빗랩 (HabitLab)" (matching
  the console exactly), and the title, meta description and a new About
  section carry an English description of the app purpose and its use of
  Google account data.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/templates/base.html

@@ -5,7 +5,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover" />
   <title>{% block title %}해빗랩{% endblock %}</title>
   {# 구글 OAuth 브랜딩 심사는 홈페이지에서 앱 이름과 목적을 확인한다 — 설명 메타 태그가 없으면 "앱의 목적에 관한 설명이 없다"로 반려된다. #}
-  <meta name="description" content="{% block meta_description %}해빗랩은 만들고 싶은 습관과 끊고 싶은 습관을 요일 단위로 관리하는 습관 기록 앱입니다.{% endblock %}" />
+  <meta name="description" content="{% block meta_description %}HabitLab (해빗랩) is a habit tracking web app. 해빗랩은 만들고 싶은 습관과 끊고 싶은 습관을 요일 단위로 관리하는 습관 기록 앱입니다.{% endblock %}" />
 
   <link rel="manifest" href="/static/manifest.json" />
   <meta name="theme-color" content="#d97757" media="(prefers-color-scheme: light)" />