chore: add GitHub issue templates

[peb-peb]

Summary

The repo has no issue templates, so incoming issues arrive unstructured. Add GitHub issue templates under .github/ISSUE_TEMPLATE/ to standardise bug reports and feature requests.

Tasks

• .github/ISSUE_TEMPLATE/bug_report.md (or .yml form) — steps to reproduce, expected vs actual, environment (browser/OS), screenshots.
• .github/ISSUE_TEMPLATE/feature_request.md (or .yml form) — problem, proposed solution, alternatives.
• .github/ISSUE_TEMPLATE/config.yml — set blank_issues_enabled and optionally a contact link.
• Apply sensible default labels (e.g. bug, enhancement) via template front-matter.

Acceptance criteria

• "New issue" shows a template chooser with Bug report and Feature request options.

Notes

• Prefer the newer YAML issue forms (.yml) for structured, required fields — but Markdown templates are fine as a first pass.