feat: Add environment configuration and Gitea OAuth

This commit introduces environment configuration and Gitea OAuth
authentication.

- Added a `.env.sample` file for configuring server settings,
  database connection, authentication, and OAuth.  This allows
  for easier customization and separation of configuration from
  code.

- Implemented Gitea OAuth for user authentication.  This provides
  a secure and convenient way for users to log in using their
  existing Gitea accounts.

- Created a troubleshooting guide to help users resolve common
  issues, including authentication and server problems.  This
  improves the overall user experience.

- Added a debug controller and view to aid in development and
  troubleshooting. This provides developers with more tools to
  investigate issues.

- Improved the user interface for login and registration. The
  changes include a cleaner design and clearer instructions.  This
  enhances the user experience.

src/views/base.html

@@ -31,6 +31,9 @@
                 </ul>
                 <ul class="navbar-nav">
                     {% if user_json %}
+                    <li class="nav-item">
+                        <span class="nav-link">Hello, {{ user.name }}</span>
+                    </li>
                     <li class="nav-item">
                         <a class="nav-link" href="/logout">Logout</a>
                     </li>