feat(stellar-wallet-snap): attach optional memo on confirmSend build flow

[khanti42]

Explanation

Context: WPN-2033 / WPN-2035 — first slice of Stellar memo support for Unified Non-EVM Send. Snap-only (no extension memo field in this PR).

Problem: confirmSend could not attach a Stellar memo to the built envelope. Exchange-style numeric memos need Memo.id; free-text needs Memo.text (≤ 28 UTF-8 bytes).

Solution: Optional memo / memoType on confirmSend. resolveStellarMemo maps explicit type, else all-digit uint64 → Memo.id, else Memo.text. Wired through TransactionBuilder / TransactionService / confirmation transaction refresh. No UI, no RequiresMemo recovery.

Out of scope (follow-ups): Snap Add/Update memo UI + recoverable RequiresMemo (WPN-2034 / WPN-2036); dialog XDR handoff (WPN-2039); muxed (WPN-2037).

Note: When memoType is omitted, all-digit values become Memo.id (Freighter-style). Digits intended as text must pass memoType: "text".

References

• Fixes: WPN-2035
• Story: WPN-2033
• Related: WPN-2038 (tests for attach path included here)

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed (no changelog — not user-facing until memo UI; MetaMask does not pass memo today)
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them (N/A — additive optional params only)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
96.2% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud