feat: UX/SAAS 12-point redesign
- auth: self-registration (role=user); first-created-user becomes super_admin
- roles: super_admin may promote others; regular admin cannot see super_admin accounts
- products: user-created private groups; admin 'สินค้าขององค์กร' (shared) with hidden/public; users can create groups
- analytics: team + per-user weak areas, close-rate-by-difficulty buckets, 30-day default, weekly trend, trainee table, active users; dashboard redesigned
- files: docx + xlsx upload support (python-docx + openpyxl)
- ui: tabs การฝึก→ผลการฝึก→ภาพรวม; admin lands on ภาพรวม / user on การฝึก; guide in topbar
- consolidate: weak-areas merged into Results (10/page), my-personas merged into Training
- copy: บุคคลต้นแบบ→persona everywhere; clearer add-product form (A/B/C, upload-or-fill)
- report: remove ดูรายงาน UI entry (endpoint kept)
Backend 348 tests pass; frontend build + vitest clean.
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