Add boilerplate code for Deploy > Applications/Environments

What does this MR do and why?

Add boilerplate code for Deploy > Applications/Environments (https://gitlab.com/groups/gitlab-org/-/work_items/22045, https://gitlab.com/groups/gitlab-org/-/work_items/22046)

These links are added at only the organization level, as confirmed in https://gitlab.slack.com/archives/C0APU3552H3/p1779460598070049

Since this MR just creates the bare bones pages, improvement to the UI will happen in follow-ups

Behind ai_native_deploy feature flag

References

• https://gitlab.com/groups/gitlab-org/-/work_items/22045
• https://gitlab.com/groups/gitlab-org/-/work_items/22046

Screenshots or screen recordings

How to set up and validate locally

1. Enable ai_native_deploy and ui_for_organizations feature flags
2. Go to organization (e.g. http://127.0.0.1:3000/o/default/)
3. Click on Deploy in sidebar to expand it, then click on Applications or Environments
4. Confirm these are not accessible when the ai_native_deploy feature flag is disabled

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #600764