Add canonical run result envelope

[chubes4]

Summary

• Add a canonical WP_Agent_Run_Result_Envelope with shared run status vocabulary, outputs, artifact/evidence refs, replay/provenance/timestamps/error/cancellation fields.
• Add non-breaking adapters from runtime package, workflow, task run-control, and package adoption result surfaces.
• Add smoke coverage and include it in the Composer smoke suite.

Testing

• php -l src/Runtime/class-wp-agent-run-result-envelope.php && php -l src/Runtime/class-wp-agent-runtime-package-run-result.php && php -l src/Workflows/class-wp-agent-workflow-run-result.php && php -l src/Tasks/class-wp-agent-task-run-control.php && php -l src/Packages/class-wp-agent-package-adoption-result.php && php -l tests/run-result-envelope-smoke.php
• php tests/run-result-envelope-smoke.php && php tests/runtime-package-run-contract-smoke.php && php tests/workflow-runner-smoke.php && php tests/task-execution-smoke.php && php tests/package-adoption-orchestration-smoke.php
• composer smoke
• composer phpstan

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (gpt-5.5)
• Used for: implementing generic run/result envelope and tests