docs(swap): remove stale TODO(12.7) comment in claim-issuer.ts

[toon-backlog-bot]

Summary

• Removes the stale TODO(12.7) comment block on MultiChainClaimIssuerConfig.signerAddresses in packages/swap/src/claim-issuer.ts
• The described work is already done: startMill() in packages/swap/src/mill.ts builds and passes the signerAddresses map via buildSignerAddresses() (see mill.ts:786-792, and the file's own top-of-file doc comment)
• Replaces the misleading "callers must supply the map explicitly" wording with an accurate note that startMill() populates this automatically, and that the field stays optional only for callers constructing MultiChainClaimIssuer directly outside startMill()
• Comment-only change — no runtime/behavioral logic touched

Closes #32

Verification

• grep -n "TODO(12.7)" packages/swap/src/claim-issuer.ts → no match (exit 1)
• pnpm -r build → succeeds
• pnpm -r test → 130 passed, 2 skipped, 0 failed

Plan deviation

None — followed the issue's suggested plan as written.

🤖 Generated with Claude Code

[ALLiDoizCode]

Reviewed: comment-only change, verified against issue #32 and mill.ts (buildSignerAddresses() at mill.ts:787, wired into MultiChainClaimIssuer at mill.ts:792 — claim matches code). Confirmed TODO(12.7) no longer appears in claim-issuer.ts and the new wording is accurate. Changeset uses the valid empty-frontmatter form (appropriate since this has no runtime effect). PR title/body accurately describe the diff — no changes needed. No blocking issues.