feat: replace hardcoded org UUID in shortcode calls with theme-level slack-invite

Background

The academy-theme now provides an org-id shortcode (see layer5io/academy-theme#215) that dynamically extracts the organization UUID from the current learning-path page's directory path (learning-paths/{orgID}/...). It also provides a generic slack-invite shortcode at the theme level.

Current state

Any org-specific shortcode calls that hardcode the org UUID namespace (e.g. {{< your-org-uuid/slack-invite link="..." >}}) introduce a maintenance burden: if the UUID changes, all content files referencing it break.

Requested change

Once academy-theme#215 is merged and the theme version is bumped in go.mod:

1. Replace org-namespaced slack-invite calls with the generic theme shortcode:

   {{< slack-invite link="https://..." >}}
   

2. Remove any local layouts/shortcodes/{orgID}/slack-invite.html override (the theme now owns it)
3. Use {{< org-id >}} anywhere the UUID is needed as a text value in content — no more copy-pasting the UUID

Why this matters for the starter template

As the canonical starter template, academy-example should model best practices. Demonstrating the use of {{< org-id >}} and {{< slack-invite >}} instead of hardcoded UUIDs helps new academy adopters avoid the maintenance pitfall from day one.

References

• academy-theme PR: https://github.com/layer5io/academy-theme/pull/215