chat: hide plugin actions for synced customization items

[joshspicer]

Fixes #314879

What

Items from the vscode-synced-customization: scheme are backed by a synthetic plugin — purely an implementation detail of the sync mechanism. Surfacing "Show Plugin" and "Uninstall Plugin" context menu actions for those items is confusing because the plugin concept is not user-facing in this context.

How

Tightened WHEN_ITEM_IS_PLUGIN to also require that the item's plugin URI does not match the vscode-synced-customization: scheme. Since all three plugin-related menu registrations (inline trash icon, 4_modify "Uninstall Plugin", 1_open "Show Plugin") use this single constant, the suppression is automatic for synced customization entries.

const WHEN_ITEM_IS_PLUGIN = ContextKeyExpr.and(
	ContextKeyExpr.equals(AI_CUSTOMIZATION_ITEM_STORAGE_KEY, PromptsStorage.plugin),
	ContextKeyExpr.regex(AI_CUSTOMIZATION_ITEM_PLUGIN_URI_KEY, new RegExp(`^${SYNCED_CUSTOMIZATION_SCHEME}:`)).negate(),
);

Regular (non-synced) plugin items are unaffected.

[Copilot]

Pull request overview

This PR adjusts the AI Customization management UI so that plugin-specific context menu actions are not shown for synced customization items, which are internally represented via a synthetic plugin under the vscode-synced-customization: scheme.

Changes:

• Tighten the WHEN_ITEM_IS_PLUGIN when-clause to exclude items whose plugin URI uses the synced customization scheme.
• Reuse the refined when-clause across all plugin-related menu contributions (“Show Plugin”, “Uninstall Plugin”, and the inline uninstall/trash action).

Show a summary per file

File	Description
src/vs/workbench/contrib/chat/browser/aiCustomization/aiCustomizationManagement.contribution.ts	Refines plugin item visibility logic to suppress plugin actions for synced customization entries by checking the plugin URI scheme.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 0