Add stale-result regression tests for async command palette search

[VatsalSy]

Why

Command palette search can receive async responses out of order, causing stale results to replace newer queries.

Evidence

• PR JavaScript optimization: eliminate redundancy and improve performance #58 review: recommended guarding against stale async promise resolution in command-palette search flow.
• Open issue Improve JavaScript test coverage (currently at 10.75%) #53 tracks low JS test coverage; this is a high-value behavior gap within that theme.

Scope

• Add query-token (or equivalent) guard so only the latest search request may update rendered results.
• Add targeted test(s) that simulate out-of-order async completions.
• Keep tests focused on behavior, not implementation internals.

Acceptance Criteria

• Rapidly typed queries cannot be overwritten by slower, older search responses.
• Test suite includes deterministic stale-response regression coverage for command palette search.
• Issue Improve JavaScript test coverage (currently at 10.75%) #53 can reference this as one concrete coverage increment.