Include full outcome-weight/seed audit columns in the anonymous-votes CSV export

[Ehonrie]

Difficulty: Advanced
Category: Feature

Context: buildDecodedVotesCsv already exports outcomeWeights/outcomeSeeds joined with /, but flattens all three outcomes into single cells, making the export hard to consume programmatically for independent audit tooling (e.g., a third party re-verifying tallies from the CSV alone without re-running the dapp's JS).

// dapp/src/utils/anonymousVotingCsv.ts
export function buildAuditableDecodedVotesCsv(
  decodedVotes: DecodedVote[],
  proposalId: number,
  proofOk: boolean | null | undefined,
): string {
  // !todo: Emit one column per outcome per field (Approve/Reject/Abstain x Weight/Seed)
  //        instead of slash-joined cells, so the CSV can be parsed and re-verified
  //        without re-implementing the "/" split logic.
  // !todo: Must include proposalId and proofOk as either header metadata or per-row
  //        columns so the export is self-describing/auditable in isolation.
  // !todo: Must remain compatible with escapeCsvValue's existing quoting rules for
  //        embedded commas/quotes/newlines in address or vote fields.
  // !todo: Acceptance: a third party with only this CSV + the public tally formula
  //        must be able to reproduce talliesArr/seedsArr from anonymousVoting.ts.
  throw new Error("Not implemented");
}

What contributors need to know:

• Problem: anonymousVotingCsv.ts:1-34 — current export is human-readable but not machine-re-derivable without parsing slash-separated cells.
• Related code: DecodedVote interface in anonymousVoting.ts:53-62.
• Suggested approach: expand CSV_HEADERS to explicit per-outcome columns; keep the existing function as a "compact" export option if UI still needs it.
• Acceptance criteria: a round-trip test that reconstructs tally totals purely from the new CSV output matches computeAnonymousVotingData's in-memory tallies for the same fixture.