095 reject bare literal arg

// ============================================================================
// Test 210_095: MUST_ERROR — a BARE literal argument must be REJECTED; a
//   literal cannot be punned, so it REQUIRES an explicit label. Bare-side
//   twin of 210_091's legal `echo(v: 5)`.
//
//   `echo(5)` is none of the three legal forms (5 is not an Expr-typed first
//   param, not explicitly named, and cannot pun). The legal spelling is
//   `echo(v: 5)`.
//
// CURRENT BEHAVIOR (the bug this pins): compiles clean — a bare literal is
//   bound positionally to parameter[0]. RED until the frontend rejects it.
//   Diagnostic is a design call; expected_patterns below is the target.
// ============================================================================

~import std/io

~tor echo { v: i32 } -> i32

~echo -> v

~echo(5): r |> std/io:print.ln("{{ r:d }}")