[Epic] OSS launch readiness

## Goal
Make the repository welcoming and safe for external contributors.

## Checklist
- [x] MIT LICENSE
- [x] CONTRIBUTING.md
- [x] SECURITY.md
- [x] Issue templates + labels
- [x] CI workflow (`.github/workflows/ci.yml`)
- [ ] Enable GitHub Discussions
- [ ] Add CODEOWNERS (optional)
- [ ] Publish a CHANGELOG / release notes flow

## Maintainer
[@adhikareeprayush](https://github.com/adhikareeprayush)

Start by reading the checked-in onboarding files mentioned in the checklist: `CONTRIBUTING.md`, `SECURITY.md`, `.github/workflows/ci.yml`, and `.github/ISSUE_TEMPLATE/*` (plus any existing `CODEOWNERS` if present). Compare them with the checklist and mark what is missing for unchecked items. Next, verify the repo-level pieces (labels/templates and Discussions settings) and the chosen changelog/release-notes flow location. A finished state is all remaining items completed, with the requested files/settings/configs in place and aligned with the checklist.

由索引模型根據 Issue 內容生成。