[codex] Require client snippet file proof

[Atomics-hub]

What changed

• Strengthened the Claude/Codex/Cursor release-ticket objective to parse the actual packaged Claude MCP JSON artifact.
• Required the Claude snippet to use command: sh and point at bin/agentk-sidecar.
• Required the actual Codex/Cursor command artifact to document the packaged sidecar, package check, safe-agent demo, dashboard, dashboard server, and store sync commands.

Why

The client handoff report already summarized these checks, but the installable sidecar objective should also verify the concrete snippets a reviewer copies into Claude, Codex, or Cursor.

Validation

• cargo fmt --check
• cargo run --locked -- release-ticket --out dist/release-ticket-client-snippet-proof --force --json | jq '{ready, client: (.checks[] | select(.name=="objective: Claude/Codex/Cursor sidecar"))}'
• cargo test --locked release_ticket_delivery_dry_run_validator_requires_local_placeholder_proof
• cargo test --locked release_ticket_smoke_inventory_lifts_named_artifacts
• cargo clippy --all-targets --all-features -- -D warnings
• cargo run --locked -- release-audit