Bounty: Add Documentation for React.js Frontend

[maxrross]

Resolves #56.

Summary

• Replace the default Vite template README with Kleo Connect-specific documentation.
• Add setup, environment variable, script, route, project structure, workflow, deployment, contributing, and troubleshooting guidance.
• Document the extension sign-in/profile validation flow and shared API request helper so new contributors can find the important entry points quickly.

Verification

• npx -y node@20 /opt/homebrew/bin/npm ci
• npx -y node@20 /opt/homebrew/bin/npm test -- --run
• npx -y node@20 /opt/homebrew/bin/npm run build
• git diff --check

npx -y node@20 /opt/homebrew/bin/npm run lint currently fails on existing Prettier/unused-code issues across the application, including files not touched by this docs-only PR. I left those code formatting changes out of scope to keep this bounty PR focused.

AI assistance disclosure

This documentation update was prepared with AI assistance and manually reviewed against the current repository structure and source files before submission.

[maxrross]

Withdrawing this PR because #79 was opened first for the same documentation bounty while I was finishing verification. This was an independently prepared docs update, but I do not want to crowd the maintainer with duplicate bounty submissions. Thanks for the consideration.