[WIP] Add login screen with email and SSO options

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>ログイン画面を実装する</issue_title>
<issue_description>- ベースはメールアドレス・パスワード認証

• Google, Facebook等での、Single Sign Onの画面も追加する。</issue_description>
• Closes ログイン画面を実装する #1

<agent_instructions>いい感じにやってください。</agent_instructions>

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