feat: add proof-carrying predictive safety plane

[pshkv]

Summary

• add SimulationReceiptV2, typed simulation preflight, tier-aware evidence enforcement, and T1 shadow calibration
• add deterministic bounded-motion simulation, ROS 2 world snapshots, durable artifacts, and an isolated HTTP worker/client
• bind receipt issuance, verification, and rejection into the append-only Evidence Ledger
• add recorded fixtures and conformance coverage for forged, stale, mismatched, unsafe, replayed, and shadow-mode evidence

Security invariants

• PolicyGateway.intercept() remains the only authorization authority
• simulation receipts never authorize execution
• T2/T3 cannot be configured into shadow mode
• receipt issuance fails closed when artifact or Evidence Ledger persistence fails
• E-stop behavior is unchanged

Validation

• 52/52 packages built
• 102/102 workspace tasks passed
• 389/389 conformance tests passed
• ROS2 latency benchmark passed

Stack

Temporarily based on #250 because this work uses the deployment-envelope foundations introduced there. Retarget to main after #250 merges.