ci: Add automated Continuous Integration workflow

[AnzalKhan16]

Description

This PR introduces a GitHub Actions Continuous Integration (CI) workflow (main.yml) to automatically validate the project on every push to main and all pull requests. The workflow checks out the code, sets up the required Python and Node.js environments, installs dependencies, and runs backend/frontend linting, tests, and builds.

Related Issues

#2370

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

This was tested by verifying the GitHub Actions configuration syntax and ensuring the specified paths for dependencies, linting, and tests align exactly with the project's structure (e.g. using ruff check, pytest, and the npm scripts typecheck, quality, test, build from the frontend/ directory). The workflow automatically runs in the GitHub environment.

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.

[utksh1]

Thank you for your interest in contributing to SecuScan.

This PR/issue is being closed for one of the following reasons:

• Duplicate functionality that already exists in the project
• Modifies critical workflows without prior maintainer discussion
• Assumes infrastructure or processes not aligned with the project

We appreciate well-thought-out contributions, but please:

1. Review existing CI/CD setup before proposing changes
2. Open an issue for discussion before submitting large PRs
3. Coordinate with maintainers on infrastructure changes

For the features we'd like to keep (Dependabot, SHA pinning, multi-arch builds, Scorecard), we'll review those PRs individually.