chore: open-source readiness — LICENSE, CONTRIBUTING, templates, package metadata

- Add MIT LICENSE
- Add CONTRIBUTING.md with setup, conventions, PR workflow
- Add GitHub issue/PR templates
- Add repository/homepage/bugs/license to all package.json files
- Add Install section to README before Quick Start

Fixes #510

小橘 🍊（NEKO Team）

.github/pull_request_template.md

@@ -0,0 +1,15 @@
+## What
+
+What this PR does.
+
+## Why
+
+Why the change is needed.
+
+## Changes
+
+- `path/to/file` — what changed and why
+
+## Ref
+
+Fixes #