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/dist/assets/Analytics-ButgVyTK.css

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+.stat[data-v-9558687f]{text-align:center;min-width:110px}.stat div[data-v-9558687f]{color:var(--muted);font-size:12px}.stat strong[data-v-9558687f]{font-size:20px}.filter-bar[data-v-9558687f]{display:flex;align-items:center;gap:10px;flex-wrap:wrap}.filter-bar input[type=date][data-v-9558687f]{width:auto}.grid[data-v-9558687f]{display:grid;grid-template-columns:repeat(auto-fill,minmax(220px,1fr));gap:14px}.tier-card[data-v-9558687f]{display:flex;flex-direction:column}.badge.won[data-v-9558687f]{background:#dcfce7;color:#166534}.badge.lost[data-v-9558687f]{background:#fee2e2;color:#991b1b}.badge.not_tried[data-v-9558687f]{background:#eef2ff;color:#4338ca}.bar[data-v-9558687f]{background:#eef0f5;border-radius:999px;height:10px;overflow:hidden;margin-top:10px}.bar-fill[data-v-9558687f]{background:linear-gradient(90deg,var(--accent),var(--accent-2));height:100%;border-radius:999px;transition:width .4s ease}.users-btn[data-v-9558687f]{background:#0ea5e9;border-color:transparent;color:#fff;font-weight:600}.users-btn[data-v-9558687f]:not(:disabled):hover{background:#0284c7;box-shadow:0 6px 16px #0ea5e959}