feat(capture): stamp redundant TSAs on deferred resolution (R-16)

[ChelseaKR]

Deferred-capture resolution now stamps against the same redundant
authorities as the online capture path, so no packet's proof rests on a
single TSA regardless of whether it was stamped at capture or resolved
later.

• capture.resolve_deferred(vault, tsa, extra_tsas=()) now calls the
  existing _stamp_additional for each queued item after the primary
  token is recorded. Extras are best-effort: an unreachable authority is
  skipped and never blocks resolution, and extras are only attempted once
  the primary has stamped. If the primary stamp fails the item stays
  deferred (unchanged error behavior). The per-item CaptureResult now
  carries extra_authorities.
• cli._cmd_resolve wires _extra_tsas_for(vault, dev=args.dev_tsa) through
  to resolve_deferred, respecting the resolve subcommand's --dev-tsa flag
  (same helper the capture command uses).
• Tests: deferred-then-resolved records the additional token and reports
  it in extra_authorities while skipping an unreachable extra; a packet
  built from a deferred-then-resolved capture reports both authorities in
  verified_authorities.
• ROADMAP: mark "Multiple-authority redundancy by default" (R-16) shipped
  now that both the online and deferred paths stamp N authorities.

Co-Authored-By: Claude Fable 5 noreply@anthropic.com

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Backfill PR for a completed roadmap item (roadmap/multiple-tsa-redundancy-by-default-r-16, 1 commit(s) over main). Part of the portfolio roadmap batch.