Closes #106: Rewrite HOME.md and Setup.md for external customer-facing audience

[simplycubed-code]

Automated change from an issue. A human reviews and merges; this loop does not.

Walkthrough

This change rewrites the repository's top-level product and setup documentation to speak to external customers rather than internal adopters. The README now presents SimplyCubed Code as a product teams install into their own GitHub, emphasizing customer control over repositories, runners, secrets, review, and merge decisions while explaining the issue-to-PR workflow in customer-facing language.

The setup guide is likewise reworked into a customer installation path. It walks a customer through installing the CLI, generating repo files, configuring the GitHub App and Azure credentials, running the one-time self-test, and operating the day-to-day issue and review loop, while removing the prior internal-project framing.

Changes

Area	Summary
Product Overview Docs	README.md reframes SimplyCubed Code as a customer-facing product overview, clarifies the deployment and trust model, and updates getting-started language around customer-owned GitHub workflows.
Customer Setup Guide	docs/setup.md turns the adopter-oriented setup notes into a step-by-step customer install and usage guide covering prerequisites, app/secret setup, self-test, and normal issue-to-PR operation.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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