repo: GitHub issue templates — bug report on GitHub, feature requests and contributing via the Maity board

tsk-mj2arrc90pgj done Maity OPS Team (maity-ops-team)

Oliver's request (2026-10-29): GitHub issue templates in .github/ISSUE_TEMPLATE/.

Bug report: an issue form (bug_report.yml) on GitHub, asking for the version (hub/CLI/web), the steps, the expected and actual behaviour, and logs without secrets.
`config.yml`: blank_issues_enabled: false, plus contact_links:
feature request → the Maity board of the project (public project page on maity.team);
want to contribute → the Maity project page (join);
security problem → SECURITY.md (private report, never a public issue).
The URLs must be the public addresses that work without signing in; check them in a private window.
Context: an entry on why bugs stay on GitHub while features and contributions go through Maity, if it is not self-evident from the files.
Changelog fragment.