Fix leaked workspaces after worker restarts

[eshulman2]

Summary

• persist ticket and repository identity inside each workspace
• delete state-recorded workspaces when the process-local manager registry is unavailable
• validate the workspace root, name, identity, and symlink status before fallback deletion
• prevent cross-repository feature workflows from deleting another repository's workspace

Validation

• uv run pytest tests/sandbox/test_task_execution.py tests/unit/workflow/nodes/test_workspace_setup.py -q (19 passed)
• uv run ruff check src/forge/workflow/nodes/workspace_setup.py tests/sandbox/test_task_execution.py
• git diff --check