i18n(th): professional, natural Thai; make Users button prominent

- Rewrite TH translations to professional/natural Thai (e.g. app 'ระบบฝึกทักษะการขาย'
  instead of 'ตัวฝึกขาย', 'บุคคลต้นแบบ' for persona, tiers 'พร้อมตัดสินใจซื้อ',
  'จุดอ่อนที่ควรฝึกเพิ่มเติม', 'ปิดการขายได้/ไม่ได้' for won/lost, etc.)
- Users button in admin overview now solid sky-blue (was faint .soft gray) so it's visible.

frontend/src/views/Analytics.vue

@@ -3,7 +3,7 @@
     <div class="row" style="align-items:center;margin-bottom:16px">
       <h2 style="margin:0">📊 {{ i18n.t('adminOverview') }}</h2>
       <div class="row" style="margin-left:auto;gap:10px">
-        <router-link to="/admin/users"><button class="soft">👥 {{ i18n.t('users') }}</button></router-link>
+        <router-link to="/admin/users"><button class="users-btn">👥 {{ i18n.t('users') }}</button></router-link>
         <router-link to="/admin/new-group"><button class="primary">＋ {{ i18n.t('addProduct') }}</button></router-link>
       </div>
     </div>
@@ -97,4 +97,6 @@ onMounted(load)
 .badge.not_tried { background: #eef2ff; color: #4338ca; }
 .bar { background: #eef0f5; border-radius: 999px; height: 10px; overflow: hidden; margin-top: 10px; }
 .bar-fill { background: linear-gradient(90deg, var(--accent), var(--accent-2)); height: 100%; border-radius: 999px; transition: width .4s ease; }
+.users-btn { background: #0ea5e9; border-color: transparent; color: #fff; font-weight: 600; }
+.users-btn:not(:disabled):hover { background: #0284c7; box-shadow: 0 6px 16px rgba(14,165,233,.35); }
 </style>