feat: dockerized the whole project

[Satvik-Singh192]

Description

This pull request containerizes the entire CollabCanvas application using Docker and Docker Compose. It fulfills the goal of the original issue (#67) by replacing the complex, multi-step manual setup with a simple, one-command startup.

Instead of requiring developers to manage two separate terminals and a manual database connection, they can now clone the repo and run:

docker-compose up --build

This PR Adds

• docker-compose.yml: Orchestrates the client, server, and db services.
• client/Dockerfile: Containerizes the Vite frontend.
• server/Dockerfile: Containerizes the Node.js backend.
• .dockerignore files: To speed up build times and ignore node_modules.
• .env.example: A root template for environment variables.
• A new "Getting Started" section in the README.md explaining the Docker-based workflow.

This PR also includes the necessary code fixes to make the app work inside the Docker environment:

• Upgraded the base image to node:20-alpine in both Dockerfiles, as required by the newer version of Vite.
• Updated the port mapping in docker-compose.yml to 3000:5173 to correctly match the Vite server.

Semver Changes

• Patch (bug fix, no new features)
• Minor (new features, no breaking changes)
• Major (breaking changes)

Issues

Closes #67

Checklist

• I have read the Contributing Guidelines.

[Satvik-Singh192]

@Ayushivam22 please review my pull request sir, thanks