chore: add CONTRIBUTING, PR template, and CODEOWNERS to require PRs

.github/CODEOWNERS

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+* @Vamsi-o

.github/PULL_REQUEST_TEMPLATE.md

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+## Summary
+
+<!-- Short description of the change. -->
+
+## What changed
+- Describe what you changed and why.
+
+## How to test
+- Steps to reproduce / test this PR locally.
+
+## Checklist
+- [ ] I opened this PR from a feature branch (not main)
+- [ ] CI builds and tests pass (no CI configured yet)
+- [ ] I added/updated tests if applicable
+- [ ] I added documentation if applicable
+
+## Reviewers
+- @Vamsi-o (code owner) will be automatically requested to review.

CONTRIBUTING.md

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+# Contributing to BuildFlow
+
+Thank you for contributing! To keep the project stable and reviewable, follow these rules:
+
+1. Branches and commits
+   - Always create a branch for your work; do not commit directly to `main`.
+   - Use descriptive branch names like `feature/add-x` or `fix/issue-123`.
+
+2. Pull Requests
+   - Open a Pull Request from your branch into `main`.
+   - Use the PR template (.github/PULL_REQUEST_TEMPLATE.md). Describe the change and how to test it.
+   - A Code Owner review is required (see .github/CODEOWNERS) — @Vamsi-o is requested by default.
+   - The `ci` status check is not required yet; CI will be added later.
+
+3. Reviews and merging
+   - A code owner (or an assigned reviewer) should approve the PR before merging.
+   - Once approved, a maintainer can merge the PR into `main`.
+
+4. Issues
+   - Open an issue before implementing non-trivial changes to discuss design and scope.
+
+If you'd like stricter automation (e.g., required status checks, automatic merges after approval), we can add CI and automation in a follow-up PR.