i18n: change all page titles and nav text to Chinese

app/templates/dashboard.html

@@ -1,5 +1,5 @@
 {% extends "base.html" %}
-{% block title %}Dashboard - Postcard Manager{% endblock %}
+{% block title %}总览 - 明信片管理器{% endblock %}
 {% block content %}
 <div class="section-header">
     <h1>👋 欢迎，{{ user.username }}</h1>
@@ -94,7 +94,7 @@
     </div>
 
     <div class="dash-section">
-        <h2>Profiles</h2>
+        <h2>Profile</h2>
         <div class="dash-profiles">
             {% for p in profiles %}
             <a href="/profiles/{{ p.id }}/postcards" class="dash-profile-link">