feat: add admin password change via /settings page
Backend:
- DB: add UpdateAdminPasswordHash(id, hash) in queries_users.go
- Auth: add ChangePassword(username, old, new) method that verifies
old password, validates length >= 8, and stores bcrypt hash
- Handlers: add handleChangePassword on PUT /api/auth/password (auth required)
- Router: register route inside protected group
Frontend:
- api.ts: add changePassword(oldPassword, newPassword)
- Settings.tsx: new page with form (current + new + confirm), client-side
validation, success/error feedback
- App.tsx: add /settings route
- Layout.tsx: add 'Ajustes' nav item
darroyo
72a8336087