fix(docker): add comprehensive .dockerignore

[sonusharma6-dsa]

Adds a comprehensive .dockerignore to avoid leaking secrets and reduce Docker image size.

[sonusharma6-dsa]

Summary: Adds a comprehensive .dockerignore to avoid leaking secrets and reduce Docker image size.

Main patterns included: Python caches/venvs, .env* files, node_modules, IDE files (.vscode/.idea), docs, and common build/temp artifacts.

Notes:

• This only prevents future files from being copied into Docker contexts; it does NOT remove already-committed secrets from history.
• Recommend re-requesting the Copilot reviewer for automated checks.
• Optional: run a quick scan for accidentally committed secrets (I can run one and report findings).

If you'd like, I can also add extra ignores or run the secrets scan now.

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[sonusharma6-dsa]

Could you please re-request the Copilot PR reviewer on this PR? The previous Copilot run errored out, and a fresh automated review would help confirm the .dockerignore update is safe.