feat(cli): extend status JSON output for CI usage

[12122J]

Closes #329

Summary

• Extends the existing codegraph status --json output with indexPath, lastIndexed, agentCount, and version
• Preserves existing JSON fields so current consumers keep working
• Reports uninitialized projects with the same machine-readable CI fields
• Uses a database aggregate for lastIndexed instead of scanning file records in the CLI

Test plan

• npm run build
• node dist/bin/codegraph.js status /tmp/codegraph-status-json-smoke --json
• npx vitest run __tests__/sync.test.ts attempted locally, but this machine is on Node v20.20.0 and the suite requires Node 22.5+ for node:sqlite; Git-backed cases also hit sandboxed git spawn EPERM here