dsh-fovea v0.2.0

Parity pass with pi-fovea v0.18.0

• sync.ackClean parity surface (default false; clean-sync ack can never restart an idle agent)
• AGENTS.md + docs/heat-diffusion.md engine design port
• scripts/probe.ts buildless dev probe via tsx
• 152 tests across 17 files; typecheck, build, and package verifier pass