chore: add contribution governance docs and dotenv dependency

.github/PULL_REQUEST_TEMPLATE.md

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+## Summary
+
+Explain what changed in this PR.
+
+## Why
+
+Explain the problem this PR solves.
+
+## Type of change
+
+- [ ] feat
+- [ ] fix
+- [ ] docs
+- [ ] refactor
+- [ ] chore
+- [ ] test
+
+## Scope
+
+What areas are affected?
+
+- [ ] API routes
+- [ ] Auth / access control
+- [ ] Database schema / migration
+- [ ] UI / UX
+- [ ] Documentation
+- [ ] Other
+
+## Validation
+
+- [ ] I ran `bun run check`.
+- [ ] I ran `bun run db:generate` if `prisma/schema.prisma` changed.
+- [ ] I manually tested affected flows.
+
+Validation notes:
+
+```text
+Paste command output or manual test notes here.
+```
+
+## Breaking changes
+
+- [ ] No breaking changes
+- [ ] This PR introduces a breaking change (describe below)
+
+If breaking, explain migration path:
+
+## Database / migration notes
+
+If schema changed, summarize migration impact.
+
+## Screenshots / examples (if relevant)
+
+Add screenshots or API request/response examples.
+
+## Checklist
+
+- [ ] PR title follows Conventional Commits (`type(scope): summary`).
+- [ ] I used `successResponse` / `apiErrors` for API response changes.
+- [ ] I used `auth()` and shared access checks (`checkProjectAccess` / `checkWorkspaceAccess`) where relevant.
+- [ ] I updated docs when behavior changed.
+- [ ] No secrets or unrelated file changes are included.