Update README with comprehensive project overview and setup instructions

[Copilot]

Refreshed root README to help contributors quickly understand and run the multi-language projects in this repository.

Changes

• Overview & Structure

  • Added project purpose, tech stack summary (Node.js, .NET, Java, Python, C++)
  • Repository structure diagram showing exercisefiles/, challenges/, and completesolution/ organization
  • GitHub Copilot keyboard shortcuts reference

• Quickstart

  • GitHub Codespaces setup (recommended path)
  • Local dev container instructions
  • Technology-specific prerequisites when not using containers

• Run Commands

  • Per-language examples: Node.js, TypeScript, .NET, Spring Boot, Quarkus, C++, Python
  • Testing table mapping each stack to its test framework and command

• Contributing

  • Contribution workflow (fork, branch, PR)
  • Code style expectations by language
  • Links to LICENSE, SECURITY.md, SUPPORT.md, CODE_OF_CONDUCT.md

• Navigation

  • Direct links to all exercise READMEs and challenge documents
  • Table of contents for quick scanning
  • External resources (MS Learn modules, Copilot docs, certifications)

All file references and commands verified against actual repository structure and dev container environment.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update README with project overview and setup instructions</issue_title>
<issue_description>The root README needs a refresh to help new contributors quickly understand and run the projects in this repo.

Scope

• Add a concise project overview (purpose, tech stack, high-level folder structure)
• Quickstart section: prerequisites, dev container notes, setup steps
• How to run: minimal commands for key subprojects (Node, .NET, Java/Quarkus/Spring, C++)
• Testing: how to run tests where available
• Contribution guidelines: link to existing policies, basic code style, and PR expectations
• Reference existing files: LICENSE, SECURITY.md, SUPPORT.md, CODE_OF_CONDUCT.md
• Links to challenge folders and example apps

Acceptance Criteria

• README includes an overview, Quickstart, run/test instructions, and contribution guidance
• All repository file links and folder references are valid
• Commands are verified to work in the dev container environment
• Clear, scannable structure with headings and short lists

Optional

• Badges (build/test status if applicable)
• Screenshot(s) or GIF(s) to preview sample apps</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Update README with project overview and setup instructions #7

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