feat(frontend): add offline and reconnect state for transfer mutations

[arisu6804]

Problem

A disconnect during signing or confirmation can cause blind retries or make a completed transfer appear failed.

Objective

Deliver a production-quality improvement to network detection, transfer status, and reconnect handling that creates measurable value for correctness, security, reliability, performance, or maintainability.

Implementation scope

• Block unsafe new mutations offline; preserve safe operation references; reconcile status on reconnect and distinguish unknown from failed.

Acceptance criteria

• Reconnect performs status lookup without duplicate submission; offline messaging is honest; sensitive data is not persisted unnecessarily.

Required validation

• Offline, reconnect, refresh, timeout, and duplicate-prevention 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.

[waterWang]

I'll work on this issue. Adding offline detection to block unsafe mutations, inline status messaging, and reconnect reconciliation.