test(frontend): add contract-driven tests for vesting, status, and precision displays

[arisu6804]

Problem

UI regressions can silently misstate withdrawable amounts or statuses when backend and contract schemas evolve.

Objective

Deliver a production-quality improvement to stream UI, API fixtures, and contract adapters that creates measurable value for correctness, security, reliability, performance, or maintainability.

Implementation scope

• Maintain versioned fixtures for lifecycle states, amounts, errors, and timestamps; assert precision-safe parsing and display.

Acceptance criteria

• Schema changes fail with actionable diffs; every supported lifecycle state renders correctly; tests do not require a live chain.

Required validation

• Contract fixture, component, error-state, and deterministic integration 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.