get_case with blank id returns confusing isError instead of Invalid params

[royalpinto007]

Problem

get_case with a missing/blank id returns a confusing isError payload (No case found with id ''.), while search_cases throws -32602 for blank queries. Inconsistent.

Where

src/mcp.ts (String(args.id ?? ""), no blank check).

Acceptance

Add a failing test first asserting blank/missing id yields -32602 like search_cases does. Then fix.