chore: add OSS readiness files and contributor docs

.github/pull_request_template.md

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+## Before you submit
+
+> **New feature?** Please open an issue first and get approval from the maintainers before writing any code.
+> PRs that introduce features without a prior discussion will be closed.
+>
+> **Used AI assistance?** That's fine - but make sure you've read and understood every line of the diff
+> before submitting. PRs that show no sign of self-review will be closed without detailed feedback.
+>
+> **Keep it focused.** One thing per PR. Don't bundle a bug fix with a refactor or unrelated cleanup.
+> If it's not ready, open it as a draft instead.
+
+---
+
+## What does this PR do?
+
+<!-- A short summary of the change and why it's needed. Link the issue it addresses if applicable. -->
+
+Closes #
+
+## How did you test this?
+
+<!-- Tell us what you actually did to verify this works. What did you run? What did you click through?
+     A quick note like "spun up Docker, added a book, confirmed it shows in the library" is perfect.
+     This helps us review with confidence and speeds up the merge. -->
+
+## Screenshots
+
+<!-- If this touches the UI, please include a before/after screenshot or a short screen recording.
+     You can drag and drop images directly here. -->
+
+## Anything non-obvious in the diff?
+
+<!-- Did you make any tricky decisions or trade-offs? Anything you'd want a reviewer to pay
+     extra attention to? This is your chance to guide the review. -->
+
+## Checklist
+
+- [ ] I've read through my own diff
+- [ ] This PR was discussed in an issue and has maintainer approval (for new features)
+- [ ] Lint and tests pass locally
+- [ ] No unintended files included (build artifacts, `.env`, personal configs)