feat: initial blog engine with multi-language, profile, and role system

- Gin + GORM + Tailwind CSS blog engine
- OS-aware config (Linux /etc/blog_go/, Windows ./win/etc/blog_go/)
- SQLite by default, MySQL support via config
- Auto-migrate database + seed admin user on first run
- Session-based auth (login/logout)
- i18n: Chinese/English with auto-detect + manual switch
- Avatar dropdown nav with click-to-toggle menu
- Profile page: avatar upload, edit info, change password
- Role system: admin (full access) and author (profile only)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

templates/pages/login.html

@@ -0,0 +1,46 @@
+{{define "login"}}
+{{template "header" .}}
+<section class="max-w-md mx-auto px-4 py-20">
+    <div class="bg-white rounded-xl shadow-sm border border-gray-200 p-8">
+        <h2 class="text-2xl font-bold text-gray-900 mb-6 text-center">{{index .Tr "login_title"}}</h2>
+
+        {{if .Error}}
+        <div class="bg-red-50 border border-red-200 text-red-700 px-4 py-3 rounded-lg mb-6 text-sm">
+            {{.Error}}
+        </div>
+        {{end}}
+
+        <form action="/login" method="post" class="space-y-5">
+            <div>
+                <label for="username" class="block text-sm font-medium text-gray-700 mb-1">{{index .Tr "login_username"}}</label>
+                <input
+                    type="text"
+                    id="username"
+                    name="username"
+                    required
+                    class="w-full px-4 py-2 border border-gray-300 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-blue-500 outline-none transition-colors"
+                    placeholder="{{index .Tr "login_ph_user"}}"
+                >
+            </div>
+            <div>
+                <label for="password" class="block text-sm font-medium text-gray-700 mb-1">{{index .Tr "login_password"}}</label>
+                <input
+                    type="password"
+                    id="password"
+                    name="password"
+                    required
+                    class="w-full px-4 py-2 border border-gray-300 rounded-lg focus:ring-2 focus:ring-blue-500 focus:border-blue-500 outline-none transition-colors"
+                    placeholder="{{index .Tr "login_ph_pass"}}"
+                >
+            </div>
+            <button
+                type="submit"
+                class="w-full bg-blue-600 text-white py-2 px-4 rounded-lg font-medium hover:bg-blue-700 transition-colors cursor-pointer"
+            >
+                {{index .Tr "login_submit"}}
+            </button>
+        </form>
+    </div>
+</section>
+{{template "footer" .}}
+{{end}}