#701 Tutorial 'Publish an extension': examples hardcode @stack72 collective, breaks copy-paste publish step

Affected page: https://swamp-club.com/manual/tutorials/publish-an-extension

The tutorial's example commands consistently use the literal collective name @stack72 (e.g. in swamp extension push @stack72/... and similar steps). Readers following the tutorial naturally copy-paste these examples verbatim.

When they reach the final publish step, the literal @stack72 collective doesn't belong to them, and the command fails:

18:45:42.403   fatal   error                Error: 'Extension collective "[@stack72](/u/stack72)" is not one of your collectives (@sntxrrgithub). Use one of: @sntxrrgithub'

Expected: the tutorial should use a generic placeholder (e.g. @your-collective) instead of a specific hardcoded collective, and should explicitly instruct readers to substitute their own collective before running the publish command.

Fix approach: replace the literal @stack72 references throughout the tutorial markdown with a placeholder token, and add a short callout reminding readers to swap in their own collective (visible via swamp whoami or equivalent) prior to the publish step.