fix tangled URLs: link to issues/pulls list page instead of broken rkey URLs
the PDS doesn't store sequential issue numbers — those are appview-only.
rkey-based URLs (e.g. /issues/3mft4plipuu22) render blank pages on tangled.org.
link to the list page until tangled.org exposes a JSON API for issue numbers.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>