fix: restore legacy workspace data fallback

[web3dev1337]

Summary

• restore backward compatibility for workspace data by preferring ~/.orchestrator when it clearly contains more user state than ~/.agent-workspace
• keep the rename migration for clean installs, but avoid hiding old workspaces when a sparse new directory already exists
• add path-utils coverage for the split-data scenario and log when the server chooses the legacy directory

Root cause

On this machine the renamed data directory existed but was sparse:

• ~/.agent-workspace/workspaces: 2 entries
• ~/.orchestrator/workspaces: 14 entries

The old migration only renamed ~/.orchestrator to ~/.agent-workspace when the new directory did not exist at all. Once ~/.agent-workspace existed, startup stopped migrating and the app loaded the sparse directory instead of the real legacy workspace set.

Test plan

• node --check server/utils/pathUtils.js
• node --check server/index.js
• npx jest tests/unit/pathUtils.test.js --runInBand
• npx jest tests/unit/workspaceManager.test.js --runInBand
• node - <<'EOF'
  const { getAgentWorkspaceDir, getLegacyCompatibilityState } = require('./server/utils/pathUtils');
  console.log({ resolved: getAgentWorkspaceDir(), compatibility: getLegacyCompatibilityState() });
  EOF