test(dor): cover kill's conflicting-confirmation rejection

[dormouse-bot]

Nightly survey finding: dor kill's confirmation guard in dor/src/commands/kill.ts rejects whenever the number of supplied confirmation modes is not exactly one:

const confirmations = [
  flags.confirmDangerously === true,
  flags.confirmIfRead !== undefined,
].filter(Boolean).length;
if (confirmations !== 1) {
  return { ok: false, message: 'dor kill requires exactly one confirmation mode' };
}

That single guard covers two distinct inputs — zero modes and two conflicting modes — but only the zero-mode case (kill missing confirmation output) was exercised. The two flags are declared independently (optional: true, no parser-level exclusivity), so --confirm-dangerously --confirm-if-read done together reaches this branch at runtime; nothing pinned that behavior.

This adds a kill conflicting confirmation output test passing both flags. Its output is identical to the missing-confirmation case (same error, same exit), so the snapshot matches byte-for-byte — the value is guarding the mutual-exclusivity contract against a future refactor that might, say, let --confirm-dangerously win silently instead of erroring.

Docs-adjacent, no behavior change. Verified locally: node --test test/*.test.mjs → 100 pass, 0 fail (the new ok 43 - kill conflicting confirmation output included).

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