Add lifecycle-aware visual parity capture for runtime state

## Problem
Visual parity currently compares pages after a fixed elapsed duration. Runtime components can be in semantically different states at that moment: source counters may be mid-transition while an imported editable candidate intentionally materializes a deterministic terminal state. Pixel comparison then reports a product defect even though the candidate preserves the declared stable state.

## Direction
Add a generic lifecycle-aware capture contract. A recipe step should be able to declare the visual state to compare, with explicit ready/stable hooks or normalized initial/terminal state semantics, instead of relying only on elapsed wall-clock duration. Keep WP Codebox generic and framework-agnostic.

## Acceptance
- Visual compare can wait for a declared stable lifecycle state on source and candidate.
- Existing duration-based captures remain supported.
- Timeout/readiness evidence names the requested and observed state.
- Repeated dynamic-component captures are deterministic.
- Unit and recipe-runner tests cover success and timeout behavior.

## Evidence
Automattic/blocks-engine#752 documents the Weebly counter case: source capture at 4 seconds observes transient values while deterministic candidate output uses terminal values.

## AI assistance
OpenAI gpt-5.6-sol through OpenCode analyzed the parity evidence and drafted this issue. Chris Huber remains responsible for scope and implementation decisions.

Trace the visual-compare capture path and recipe runner, then inspect the existing unit and recipe-runner tests. Define how a recipe declares a stable lifecycle state while preserving duration-based captures. Done means source and candidate captures can wait for and report requested and observed states, with deterministic repeated captures and success/timeout coverage.

Written by the indexing model from the issue text.