Add fallback mode and submission documentation

[gunjan-ghangare]

This pull request adds comprehensive user and submission documentation for the "Buy or Wait?" challenge and improves the quick start instructions. The most important changes are the addition of a detailed quick start guide, a solution architecture overview, and a submission readiness checklist, as well as streamlined instructions in the main README.md.

New and Improved Documentation:

• QUICK_START_GUIDE.md: Introduces a step-by-step quick start guide, including setup, running, validation, troubleshooting, and submission instructions. Also explains how the AI decision process works, expected output format, and tips for success.
• SOLUTION_OVERVIEW.md: Provides a thorough technical and architectural overview of the solution, covering data flow, decision logic, error handling, performance, and suggestions for future improvements.
• SUBMISSION_READY.md: Adds a submission checklist and confirmation document, summarizing what files to submit, validation status, what the solution does, and guidance for the submission process and potential interview questions.

Quick Start and Submission Process Improvements:

• README.md: Streamlines the quick start section by replacing manual steps with shell scripts (setup.sh, run.sh, create_submission.sh), clarifies required environment variables, and summarizes the output and submission process.

These additions make it much easier for users to set up, understand, validate, and submit their solution, and provide clear technical context for reviewers and future maintainers.

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