Issue #3586355: Avoid loading the full published catalog on the CCC overview page.

Description

Stops the CCC overview page from loading every published context item just to decide Getting Started UI flags.

Changes

• Add AiContextScopeIndexService::hasPublishedGlobalItem() — LIMIT 1 join on the scope index + published item data table.
• Update AiContextOverviewController to:
  • detect published items with a range(0, 1) entity query using accessCheck(TRUE)
  • detect global items via the new scope-index existence check
  • stop calling loadMultiple() on the full published catalog
• Preserve existing overview cache metadata (ai_context_item_list, ai_context.agents, user.permissions).
• Extend kernel + functional tests for the global / non-global Getting Started states.

No user-facing copy or settings behavior changes. No breaking API changes.

Testing instructions

0. Install and configure ai_context, switch to this branch, and clear cache.
1. With no published context items, visit /admin/config/ai/context/overview and confirm “There are no published context items.”
2. Create a non-global published context item and confirm “You have context, but no agent settings.”
3. Create/publish a global context item and confirm “You have context items and agent settings.” without configuring agents.
4. Delete/unpublish the global item, configure an agent assignment, and confirm the same configured Getting Started message still appears.
5. Optional: with a large published catalog, confirm overview still loads quickly and does not hydrate all items.
6. Rebuild caches if needed (drush cr). No config import required.

Automated:

ddev phpunit --filter testHasPublishedGlobalItem web/modules/contrib/ai_context/tests/src/Kernel/AiContextScopeIndexTest.php
ddev phpunit --filter testOverviewPageContentStates web/modules/contrib/ai_context/tests/src/Functional/AiContextAdminSettingsTest.php

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
• 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

Not applicatable:

• I have updated documentation for any new or changed functionality

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Closes #3586355 (closed)