[Docker] Fix incomplete Dockerfile and update README with local Docker instructions

[Suryakantdsa]

Problem

The current Dockerfile does not install dependencies (yarn install) or build the app (yarn build), making the container non-functional when built locally.

Impact

• Docker images built locally fail to run (missing node_modules).
• Contributors cannot run the app via Docker without manual workarounds.
• GitHub Actions builds the app separately, but the image doesn’t include these steps.
• Violates the principle of portable containers.

Proposed Solution

• Update Dockerfile
  • Install dependencies explicitly (yarn install).
  • Build the app inside the container (yarn build).
  • Remove redundant build steps from GitHub Actions.
• Update README.md

Hi @aryanmehrotra @aditya-tiwari-zs @satyamt05 👋.
I’d like to work on this. Please assign this issue to me.