feat(frontend): show live streamed amount with bounded polling and clock handling

[arisu6804]

Problem

A live balance display can be misleading when polling is unbounded, browser time is wrong, or the stream state has changed.

Objective

Deliver a production-quality improvement to stream detail, accrual display, and refresh behavior that creates measurable value for correctness, security, reliability, performance, or maintainability.

Implementation scope

• Use server/chain timestamps and bounded polling; show last-updated and pending states; stop polling when terminal or hidden.

Acceptance criteria

• Displayed accrual never exceeds the authoritative cap; polling is bounded; clock drift and stale status are visible.

Required validation

• Fake-clock, polling-limit, tab-visibility, terminal-state, and reconciliation 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.