feat(ci): GitLab CI/CD pipeline for same-server deployment

[thana0623]

Summary

• Add GitLab CI/CD pipeline for same-server deployment using shell runner
• Local Docker build instead of pulling from GHCR (no registry auth needed)
• override for local image builds

Changes

• : Simplified deploy job with shell runner executor
• : Build images locally from Dockerfiles

Server Setup Required

1. Register GitLab Runner with shell executor
2. Set runner tags:
3. Create on server with required variables
4. Set in root gitconfig

TODO

• Fix server repo divergence (local main vs GitHub main)
• Test full deploy pipeline end-to-end
• Add health checks and rollback support