Add a CONTRIBUTING guide and correct the stale README setup and project-layout docs

[greatest0fallt1me]

Description

The README no longer matches the codebase. It describes the app as "Main app and tabs" with a project layout listing only App.tsx, main.tsx, index.css, vite-env.d.ts (README.md:50-63), but the real app is router-driven with pages/, components/, hooks/, data/, utils/, and a ThemeContext (see src/pages/, src/components/, src/ThemeContext.tsx). It also points the design-system link and "components" guidance at docs/UI-Design-System.md (README.md:19-26) without explaining the contribution workflow, and there is no CONTRIBUTING file and no test command documented (none exists yet — package.json:6-10).

This issue refreshes the README and adds a CONTRIBUTING.md that reflects the actual structure and workflow.

Requirements and context

• Update README.md "What's included" and "Project layout" sections (README.md:11-16,50-63) to describe the real routes (/, /dashboard, /marketplace, /details/:id, /billing, /api-usage, /500) and the real src/ tree.
• Fix outdated phrasing ("Main app and tabs" — the app uses React Router, not tabs) and ensure the scripts table matches package.json (README.md:42-48).
• Add CONTRIBUTING.md covering: prerequisites (Node 18+), fork/branch naming (feature/...), running npm run dev/npm run build, the design-token rules from docs/UI-Design-System.md, theme/accessibility expectations (README.md:22-26), and a note that a test runner is being introduced (link the Vitest setup issue) with the future npm run test command.
• Non-functional: docs only — no code changes; keep links relative and valid.

Acceptance criteria

• README.md project layout reflects pages/, components/, hooks/, data/, utils/, ThemeContext.tsx.
• README lists the actual routes and removes the "tabs" wording.
• Scripts table matches package.json exactly.
• CONTRIBUTING.md exists with setup, branch-naming, design-system, and accessibility guidance.
• All relative doc links resolve.

Suggested execution

1. Fork the repo and create a branch — git checkout -b docs/contributing-and-readme-refresh.

2. Implement changes — README.md, new CONTRIBUTING.md.

3. Write/extend tests — not applicable (documentation only); the repo has no test runner configured, and this change adds none.

4. Test and commit —

npm install
npm run build    # confirm docs changes don't affect the build
npm run dev      # spot-check that documented routes load

Example commit message

docs: refresh README structure and add CONTRIBUTING guide

Guidelines

• Documentation accuracy over coverage here; ensure every documented path/route actually exists in the repo.
• Keep guidance consistent with docs/UI-Design-System.md and the accessibility expectations already stated in the README.
• Timeframe: 96 hours.

[AnnieIj]

Hi maintainer, I can handle this. I’ve worked on improving project documentation and contributor onboarding, so I can create a clear CONTRIBUTING.md guide and update the outdated README and project structure documentation to reflect the current state of the codebase.

[Tolais]

Hello, maintainer, I can work on this issue and submit PR in no time.