feat(frontend): add offline and reconnect behavior for active streams

[arisu6804]

Problem

A disconnect can freeze accrual displays or lead users to resubmit mutations without knowing their status.

Objective

Deliver a production-quality improvement to network state and active stream views that creates measurable value for correctness, security, reliability, performance, or maintainability.

Implementation scope

• Show offline/stale state; stop unsafe mutation attempts; reconcile active streams on reconnect using durable references.

Acceptance criteria

• Offline views are honest about freshness; reconnect does not duplicate operations; sensitive state is not persisted unnecessarily.

Required validation

• Offline transition, reconnect, refresh, 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.