merge: integrate dev into main

[eshulman2]

Summary

Integrates the current dev line into main as the base of the declarative-workflow PR stack.

This includes:

• concurrent CI and review-gate routing
• provider-neutral source-control contracts
• the GitHub source-control adapter and normalized event transport
• conflict resolutions against the current main workflow and workspace recovery behavior

Stack

1. This PR: main ← integration/dev-to-main
2. prototype: declarative runtime-compiled workflows #317: declarative runtime-compiled workflows
3. prototype: layered planning state #318: layered planning state

Verification

• uv run ruff check src
• make test-pr: 2727 passed

Notes

The existing unrelated test warning about an un-awaited AsyncMock in test_fetcher.py remains.