Add SDK signed transaction inspection utility

[El-swaggerito]

Description

Difficulty: Expert

Type: Feature

Summary

Add a utility for inspecting signed transactions before submission.

Current Behaviour

Consumers may need to confirm transaction details after signing but before submission.

Expected Behaviour

The SDK should expose safe readable metadata without leaking sensitive internals.

Suggested Implementation

Create a helper that summarises source account, operation count, memo, fee, network, and hash where available.

Files or Areas Likely Affected

src/transactions/
src/wallet/
src/types/
tests/

Acceptance Criteria

• Signed transaction summary helper is added.
• Summary includes useful metadata.
• Sensitive values are not exposed.
• Tests cover valid and invalid signed transactions.
• Documentation includes an example.

Additional Notes

This supports better review and debugging flows.

[XxHugheadxX]

Reviewed the code before applying — the pieces are already there, just never
connected. A few things I confirmed that shape my approach: SignedTransaction in
src/transactions/offline-preparation.ts:160 already carries transaction,
networkPassphrase, hash and the full signed xdr, but nothing summarises it, while
mapTransactionToSummary in src/transactions/mapper.ts builds TransactionSummary
only from Horizon records — so you can summarise a transaction you fetched, never
one you just signed. The subtle part is what "sensitive" means here: diagnostics,
merged in #324, defines DIAGNOSTICS_SENSITIVE_KEYS listing xdr, envelope,
signature and signedXDR as always-redacted, so the field SignedTransaction
exposes is exactly the one the repo already classified as unsafe. I'll summarise
source, operation count, fee, memo with its type, network and hash by reading the
envelope rather than echoing it, aligning with that existing policy instead of
inventing a second one. Tests: valid and malformed envelopes, unsigned input, a
memo-type case, and an assertion that no sensitive key leaks into the summary.

[grantfox-oss]

🦊 GrantFox — @XxHugheadxX has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #206)
2. Your PR will be reviewed by the Axionvera maintainers

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