refactor: docker image for less final size (#315)

[nahSystemu]

This pull request introduces a comprehensive overhaul of the Docker build and deployment process for the web application, resolving issue #315 , focusing on improved Dockerfile layering, distroless production images, runtime environment variable injection, and robust database migration handling. It also enhances the .dockerignore for more efficient builds and updates the docker-compose.yml to support the new workflow. Additionally, there are minor improvements to authentication environment variable handling and Next.js configuration.

Docker build and deployment improvements:

• Refactored apps/web/Dockerfile to use a multi-stage build, including Alpine-based build stages, a dedicated migration stage, and a final distroless production image for enhanced security and smaller image size. Added a custom bootstrap.cjs script to inject runtime environment variables and start the Next.js server.
• Added a new migration service and healthchecks in docker-compose.yml, ensuring that database migrations run as a one-off container before starting the web app, and that the web app waits for migration completion.

Build efficiency and configuration:

• Expanded and reorganized .dockerignore to exclude unnecessary files and directories, reducing Docker build context size and improving build times.
• Updated apps/web/next.config.js to exclude dev-only dependencies from the standalone output, reducing production image size.
• Minor fix to image loader configuration in next.config.js for consistency.

Authentication and environment handling:

• Improved handling of trusted origins in packages/auth/src/auth.ts by filtering out empty values from the environment variable.

Final breakdown of build images:

Image	Size	Change
ghcr.io/kanbn/kan (official)	2.84 GB	—
ghcr.io/kanbn/kan (distroless)	343 MB	-87.9%
ghcr.io/kanbn/kan-migrate (alpine)	240 MB	new
Combined total	583 MB	-79.5%

[nahSystemu]

Tried to get the build to stop, since it froze on a step for 4 hours

[nahSystemu]

Shit, it launched another build