Adds a new static page accessible at /changelog to display site updates and changes manually.
- Creates a new Flask Blueprint in `routes/changelog.py` to handle the route logic.
- Registers the `changelog_bp` blueprint in `app.py`.
- Creates the corresponding template `templates/changelog/changelog.html` extending the base layout.
- Adds a link to the Changelog page in the main sidebar navigation in `templates/base.html`, using an archive icon for consistency.
- Applies basic card styling to the changelog page content for improved visual structure.
