docs: add contribution guidelines and pull request template

[nightt5879]

Summary

• Add an English contribution guide covering community language, development checks, pull request expectations, and AI-assisted contributions.
• Add a pull request template for validation evidence, AI disclosure, and contributor responsibility.
• Establish a lightweight and consistent contribution process for the Drawnix community.

Related Issue

None.

Validation

• Applicable checks pass: lint, format check, tests, and build
• Relevant E2E and manual tests are complete or not applicable

Evidence, screenshots, or compatibility notes:

• npm run lint passed locally.
• npm run test passed locally: 4 projects and 29 tests.
• npm run build passed locally: 4 projects.
• npm run format:check reported existing Windows workspace formatting differences across 128 files; neither added Markdown file was reported. The same check passed in Linux CI.
• The main CI job passed, including lint, format check, affected tests/builds, and E2E.
• E2E and manual product testing are not applicable to this documentation-only change.

AI Assistance

Did you use AI tools to generate or substantially modify code, tests, or documentation in this pull request?

• No
• Yes

If yes:

• Tool/model: Codex / GPT-5.6 Sol

• AI-assisted work: I used Codex to review the current repository workflow and settings and to draft and refine CONTRIBUTING.md and the pull request template based on my requirements.

• My review and validation: I reviewed the complete contents of both documents, confirmed the policy and scope, and approved the final drafts. I also reviewed the repository commands and settings and the reported results from the local lint, tests, and builds.

• I reviewed and understand the AI-assisted changes and can explain and maintain them

Checklist

• The title and description are in English, and the change is focused
• I reviewed and understand every submitted change
• Tests, documentation, and translations were updated when needed

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[nightt5879]

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Pull request overview

Adds baseline community contribution documentation and a PR template to standardize expectations for development checks, PR content, and AI disclosure across the Drawnix repository.

Changes:

• Add CONTRIBUTING.md describing community language, local dev checks, PR expectations, and AI-assisted contribution requirements.
• Add .github/pull_request_template.md to capture summary, validation evidence, and AI disclosure consistently.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
CONTRIBUTING.md	Introduces contributor workflow guidance (language, local dev checks, PR expectations, AI disclosure).
.github/pull_request_template.md	Adds a PR template to standardize validation evidence and AI-assistance disclosure.

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[pubuzhixing8]

Thanks for the contribution! This looks good overall. Approved. As a non-blocking follow-up, please consider adding a link to CONTRIBUTING.md in both README.md and README_en.md so contributors can discover the guide more easily.

[nightt5879]

Thanks! I’ve added the CONTRIBUTING.md link to both README files. Could you take one more look? If everything looks good, I’ll merge this PR and then set up the same contribution process for Plait.

[pubuzhixing8]

LGTM!