feat: use @adonisjs/auth with custom MikroORM user provider

[B4nan]

Summary

• Replace custom JWT auth with AdonisJS's built-in @adonisjs/auth package using SessionUserProviderContract backed by MikroORM
• Add MikroOrmUserProvider that bridges MikroORM's EntityManager with the AdonisJS session guard
• Use route groups with named auth middleware instead of controller-level auth checks
• Use ctx.auth.use('web').login(user) and ctx.auth.getUserOrFail() in controllers
• Tests use loginAs(user) helper instead of manual JWT bearer tokens
• Remove custom JWT service, auth utility, and HttpContext type augmentation

Test plan

• All 11 existing tests pass (sign in, sign up, profile, CRUD articles, comments)
• Manual smoke test of sign-in/sign-up flow
• Verify session cookie is set on sign-in response

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