feat: add GitHub Issues Integration to community catalog (#2188)

* feat: add GitHub Issues Integration to community catalog

Add GitHub Issues Integration extension to the community catalog and README.

Extension provides:
- /speckit.github-issues.import - Import GitHub Issue and generate spec.md
- /speckit.github-issues.sync - Keep specs updated with issue changes
- /speckit.github-issues.link - Add bidirectional traceability

Resolves #2175

* Modify created_at and updated_at timestamps

Updated timestamps for created_at and updated_at fields.

* Update updated_at date in catalog.community.json