docs: update architecture review with measured results

Phase 9 of architecture redesign:

- Run final statistical benchmarks (count=5) and generate benchstat
  comparison against Phase 0 baseline

- Add Section 10 "Architecture Redesign Results" to
  docs/architecture-review.md with:
  - Summary table of all 8 implementation phases
  - Benchstat latency comparison (POST sync path -33%, Petstore -11.5%)
  - Benchstat allocation comparison (-8 allocs/op for body validation)
  - Benchstat memory comparison (-10% for Petstore, -5.7% for BulkActions)
  - Analysis of GET path regression (+5 allocs, acceptable tradeoff)
  - Remaining optimization opportunities

- Save final benchmark results to benchmarks/results/current.txt

All existing tests pass. No code changes in this phase.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: its-hammer-time