feat: add workflow run await service

[chubes4]

Fixes #421

Summary

• add WP_Agent_Workflow_Run_Awaiter with explicit, storage-agnostic WP_Agent_Workflow_Run_Recorder dependency injection
• perform a fresh lookup, skip drain work for terminal runs, and compose suspended runs with WP_Agent_Workflow_Scoped_Drain
• return normalized agents-api/workflow-run-await/v1 state with canonical terminal results and unchanged scoped-drain stats
• keep budget/limit exhaustion and reentrant refusal successful and reconnectable while preserving failed terminal state

Consumer context

Consumers that own workflow-run persistence can now await their recorded runs through a shared generic PHP service without duplicating drain composition. The contract adds no storage implementation, ambient resolver, REST ability, global dependency, or consumer/product vocabulary.

Tests

• php -l src/Workflows/class-wp-agent-workflow-run-awaiter.php
• php -l tests/workflow-run-awaiter-smoke.php
• php tests/workflow-scoped-drain-smoke.php
• php tests/workflow-run-awaiter-smoke.php
• php tests/bootstrap-smoke.php
• composer smoke
• composer phpstan (not run: phpstan binary is not installed in this isolated worktree)

AI assistance

• AI assistance: Yes
• Tool(s): OpenAI GPT-5.6 Sol via OpenCode; general coding subagent
• Used for: Architecture analysis, implementation, and behavioral tests.