feat(frontend): make quote freshness and currency validation explicit in send flow

[arisu6804]

Problem

Users can confirm a transfer using an expired quote or an amount/currency combination that the backend will reject.

Objective

Deliver a production-quality improvement to FX quote selection, amount entry, and send confirmation that creates measurable value for correctness, security, reliability, performance, or maintainability.

Implementation scope

• Show quote source, timestamp, expiry, currency metadata, and canonical amount; invalidate on field/network changes; bind quote ID to payload.

Acceptance criteria

• Expired or mismatched quotes cannot be signed; displayed and serialized amounts reconcile; refresh behavior is clear.

Required validation

• Expiry, currency matrix, precision, changed-input, and quote-binding tests.
• Existing tests and CI remain passing.
• Add regression coverage for the original failure mode.
• Do not weaken, delete, or skip unrelated tests to obtain a green build.

PR quality bar

• Keep the PR focused and explain design tradeoffs, compatibility impact, and test evidence.
• Avoid typo-only, documentation-only, cosmetic-only, or unrelated refactor submissions.

Out of scope

• Broad rewrites not required by the acceptance criteria.
• Changes to unrelated services, contracts, or user flows.

[grantfox-oss]

🦊 GrantFox — @euniceamoni has been assigned to this issue as part of the Third Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #279)
2. Your PR will be reviewed by the RemitFlow maintainers

Good luck! Track your progress on GrantFox.