Issue #3586264: Show warning when subcontext parent is unpublished.

Description

See issue:

[Discuss] Moderation status of subcontext vs pa... (#3586264) • Kristen Pol • 1.0.0-beta3

Testing instructions

1. Install ai_context dev branch per project page
2. Switch to this MR branch
3. Create a context item that's published
4. Create a subcontext item that's published
5. Re-edit the subcontext item, no warning
6. Change the parent to published
7. Re-edit the subcontext item, warning

Checklist

• I have updated the MR title to use format: Issue #1234: My issue title.
• I have updated the MR description to include: Closes #1234
• I have performed a self-review of my own code
• I have added or updated tests, or explained in the description why this change is not covered by tests
• I have written testing instructions and verified them locally

Not applicable:

• I have updated documentation for any new or changed functionality
• I have noted any required post-merge steps (config imports, cache rebuilds, manual changes)
• This MR contains no breaking API or hook changes, or they are explicitly documented in the description

AI Compliance

Note

Check the one that best describes your usage, or leave all unchecked if AI was not significantly used.

• AI Assisted Code
  Mainly written by a human; AI used for autocomplete or partial generation under full human supervision.

• AI Generated Code
  Mainly generated by AI, reviewed and approved by a human before this MR was created.

• Vibe Coded
  Generated by AI and only functionally reviewed before this MR was created.

Closes #3586264