shell-quote `quote()` does not validate object-token shapes, allowing command injection via line terminators in `.op`

shell-quote's quote() function did not validate object-token inputs against the operator model used by parse(). The .op field was backslash-escaped character by character using /(.)/g, which in JavaScript does not match line terminators (\n, \r, U+2028, U+2029). A line terminator in .op therefore passed through unescaped into the output; POSIX shells treat a literal newline as a command separator, so any content after it would execute as a second command. The vulnerable code path is reachable in two ways: (1) direct construction of { op: '...\n...' } from external input, and (2) via parse(cmd, envFn) when envFn returns object tokens whose .op is attacker-influenced. Both are documented API surface. Fixed by replacing the per-character escape with strict shape validation: .op must match the parser's control-operator allowlist; { op: 'glob', pattern } validates pattern and forbids line terminators; { comment } validates comment and forbids line terminators; any other object shape throws TypeError.