fix(full-year): keep failed full-year ZIP exports in exact-ID review

[lamemustafa]

Raised by automated review of #96 against src/background/filed-returns-full-fiscal-year.ts:354:
a failed full-year ZIP export should stay in exact-ID review rather than leaving
the run able to proceed without that evidence.

Deferred from #96 deliberately. The full-fiscal-year path is 8 modules and about
3,026 lines that have never been executed against the GST Portal, so it is
the wrong thing to change inside a PR whose verified scope is single-period
acquisition. It belongs to the full-year lane, which begins with live probing
rather than with speculative fixes.

Context for whoever picks this up

• Full-year delegates each period to the single-period runner, which is
  live-verified; the orchestration around it is what has never run.
• Full-year artifacts are staged in OPFS and do not reach chrome.downloads
  until the final ZIP, so resume must re-check OPFS presence for the
  ledger/target rather than calling downloads.search.
• GSTR-3B full-year currently returns a "not wired" step on the first line of
  startFullFiscalYearDownloadFlow, while the popup still offers "Full year" for
  all three return types.
• The period planner is date-aware: the current financial year plans 3 periods,
  not 12, which makes a current-FY run the cheapest end-to-end exercise of the
  whole orchestration.

This finding should be re-verified against live behaviour before it is
implemented, not fixed from the code alone.