Add manually-triggered preview deploy workflow and host deploy script

[Blessy7-eng]

Description

This PR adds a GitHub Actions workflow that can be triggered manually to deploy a preview version of the site via SSH. It also includes the necessary shell script to handle the deployment steps on the host server.

Changes

• Added .github/workflows/preview-deploy.yml: Uses workflow_dispatch to allow manual triggers.
• Added scripts/deploy-preview.sh: Handles git fetching, migrations, and service restarts.

Infrastructure Requirements

For this to work, the following secrets need to be added to the repository settings by an admin:

• PREVIEW_HOST
• PREVIEW_USER
• PREVIEW_SSH_KEY
• PREVIEW_PROJECT_DIR

Checklist

• Workflow file validated.
• Deployment script included.
• No conflicts with the main branch.

I noticed this was an open proposal and decided to contribute a working version.
I'm happy to adjust the script based on the specific server environment requirements!

[Blessy7-eng]

Hi! I have fixed the formatting and executable permissions for the script and workflow file. I had to force-push the changes, so the CI is currently awaiting manual approval to run again. Ready for review whenever a maintainer has a moment!