chore(agents): rewrite utoopack performance agent v2

- Self-time (exclusive) calculation via span tree reconstruction
- Build-phase timeline (resolve → parse → analyze → chunk → codegen → emit)
- Corrected tier category matching with real Turbopack span names
- Critical path detection for serialization bottlenecks
- Comparison mode (--compare) for regression detection
- TURBOPACK_TASK_STATISTICS integration (--task-stats)
- Flame graph collapsed-stack output (--flamegraph)
- Document all 4 tracing methods: TRACING_CHROME, TURBOPACK_TRACING,
  TURBOPACK_TRACE_SERVER, TURBOPACK_TASK_STATISTICS
- Add persistent caching analysis guidance
- Add Rust CLI (pack-cli) profiling path
- Fix build command: npm run build:local -w @utoo/pack

Author: xusd320