[DX] Add CONTRIBUTING.md section on running tests, linting, and submitting the first PR

[gregemax]

Summary

CONTRIBUTING.md is detailed (17 KB) and covers application requirements, branching strategy, and PR guidelines. But it is missing a quick-start section that tells a new contributor exactly which commands to run after cloning.

This is a common drop-off point: a developer who wants to contribute doesn't know if they need to run npm test, cargo test, both, in which directory, or in which order.

What's needed

Add a "Your first contribution" section near the top of CONTRIBUTING.md:

## Your first contribution — quick checklist

After cloning and running local setup (see docs/local-development.md):

### Backend
```sh
cd stellance/backend
npm test                  # run 71 unit tests — all should pass
npm run lint              # check for lint errors before committing

Frontend

cd stellance/frontend
npm test                  # if test suite exists
npm run lint
npm run build             # verify no type errors

Smart contracts

cd stellance/Contracts
cargo test                # run 30+ tests — all should pass
cargo clippy              # lint
cargo build --target wasm32-unknown-unknown --release

Before opening a PR

• All tests pass locally
• cargo clippy and npm run lint produce no errors
• No .env files committed
• PR description explains why the change is needed, not just what changed

## Additional gap

The issue templates in `.github/ISSUE_TEMPLATE/` only have contributor application forms — add a standard **bug report** and **feature request** template.

## Acceptance criteria

- [ ] Quick-start checklist added to `CONTRIBUTING.md`
- [ ] Bug report template added to `.github/ISSUE_TEMPLATE/bug-report.md`
- [ ] Feature request template added to `.github/ISSUE_TEMPLATE/feature-request.md`

## Effort

~1 hour. Great good first issue for someone who has just gone through onboarding.

[Talentgift24-ux]

📋 Grainlify Application

@Talentgift24-ux has applied to work on this issue as part of the Grainlify program.

i would love to work on this issue

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