fix(tree): hide single-item context menu commands when multiple items selected

[hanhan761]

Summary

Add && !listMultiSelection to the when clause of 36 context menu commands in the Connections tree view. When multiple items are selected, single-item commands are now hidden, preventing silent failures (commands acting on only the first item) or unexpected behavior.

Issue

Fixes #668

Approach

Followed the issue audit table exactly:

• 36 commands -- Added !listMultiSelection to when clause
• 2 commands -- Intentionally skipped (already support multi-select: removeConnection, moveItems)
• Discovery-view-only commands -- Intentionally skipped (discoveryView does not have canSelectMany: true)

Verification

• npm run build -- TypeScript compilation passes
• npm run lint -- ESLint passes
• npm run prettier-fix -- formatting confirmed

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds an asynchronously loaded index count to the “Indexes” tree node (shown in the description), and updates context menu enablement to avoid showing single-item actions during multi-selection.

Changes:

• Add background fetching + caching of index counts for a collection’s Indexes node and refresh the tree item when loaded.
• Kick off index count loading when a Collection is expanded (fire-and-forget).
• Update many view/item context menu “when” clauses to disable commands when listMultiSelection is active, and add related l10n strings.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 10 comments.

File	Description
src/tree/documentdb/IndexesItem.ts	Adds async index count loading, caching, and tree refresh + shows count in tree item description.
src/tree/documentdb/CollectionItem.ts	Starts the background count load when creating the IndexesItem.
package.json	Disables various context menu commands during multi-selection via !listMultiSelection.
l10n/bundle.l10n.json	Adds localized strings for singular/plural index count display.

[tnaum-ms]

Maintainer note (triage)

During triage this branch was rebased onto main and the index-count feature was pruned out, because that functionality already landed separately in PR #714. As a result, the earlier Copilot review comments referencing IndexesItem.ts / CollectionItem.ts / index-count localization strings no longer apply and have been acknowledged inline.

The PR now contains only the intended fix for #668: adding && !listMultiSelection to the single-item context-menu when clauses so those commands hide during multi-selection. No code beyond package.json remains.

Note for reviewers: a quick manual UI check (select multiple tree items, confirm single-item actions disappear) is recommended before merge.