Visual compare can screenshot before local stylesheets finish loading

## Problem

`wordpress.visual-compare` can produce and classify a pixel diff while local linked stylesheets are still pending. `waitForVisualComparePaintReady()` caps its load wait and stylesheet wait at 10 seconds each, even when the command has a substantially larger wall timeout. Capture diagnostics then report pending stylesheets and low-confidence readiness, but the already-written screenshots continue into comparison as if they were conclusive.

This can create a false large layout delta when a pending stylesheet owns responsive visibility or geometry.

## Expected behavior

- Use a bounded stylesheet-readiness budget derived from the visual command timeout.
- Preserve enough wall time for settling, snapshots, screenshots, and diagnostics.
- Do not classify screenshots as conclusive visual evidence when required local stylesheets remain incomplete.
- Cover delayed local stylesheet loading with deterministic tests.

## Acceptance criteria

1. A local stylesheet that completes within the derived readiness budget is applied before capture.
2. A stylesheet that remains pending after the budget produces explicit incomplete-capture evidence rather than a misleading visual-diff classification.
3. Existing external-request isolation and overall command bounds remain intact.

## AI assistance

OpenAI GPT-5.6 Sol via OpenCode diagnosed the capture evidence, traced the owning implementation, and drafted this issue under human direction.

waitForVisualComparePaintReady() から開始し、診断、安定化、スナップショット、スクリーンショットを含む wordpress.visual-compare のキャプチャパスを追跡します。決定論的なテストでローカル stylesheet の遅延読み込みを検証します。完了条件は、外部リクエストの分離を壊すことなく readiness がコマンドのタイムアウトを使用し、保留中の stylesheet が確定的な visual-diff 分類ではなく、不完全なキャプチャであることを明示する証拠を生成することです。

索引モデルが issue の本文から書いたものです。