Add navbar account access and modal with auth context

[nasmans]

Summary

• add an authentication context to share login state, modal visibility, and login/logout handlers
• implement a responsive navbar with a unified "حسابي" button that opens the account modal or redirects authenticated users
• create the account modal with a login form, close handling, and redirects for successful login and new user onboarding

Testing

• not run (not available)

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https://chatgpt.com/codex/tasks/task_b_69025eb3270c8328b932735f6e5f103a