feat(sentinel): add authenticated robot policy enforcement

[enkerewpo]

What changed

• add a typed Sentinel rule engine and ListRules / ReplaceRules management contracts
• carry a Keystone-validated session on the internal Liaison -> Pilot -> Executor path, redact it from public Plan events, and re-resolve identity before execution
• enforce robot-level rules immediately before capability dispatch using typed RFC 6901 state paths, user/role, capability, time, and region inputs
• require an authenticated Keystone admin for rule management
• advertise the Sentinel provider, validate explicit and derived listen-port collisions, and bootstrap a versioned Webots demo policy only on first run

Why

This provides the minimum end-to-end Sentinel loop for the Keystone demo branch without hard-coding robot predicates such as moving or gripper_open. Robot state remains generic and typed, so deployments can address boolean, integer-range, and float-range conditions through stable state paths.

Security properties

• caller-supplied identity is overwritten after Keystone resolution
• Executor derives canonical identity from Keystone instead of trusting Plan user/role fields
• the reusable session token is cleared from client-visible Plan events
• malformed capability arguments and missing/wrongly typed policy state fail closed
• only Keystone admins can list or replace rules

Validation

• cargo fmt --all -- --check
• cargo test -p robonix-sentinel -p robonix-executor -p robonix-cli (7 Sentinel, 44 Executor, 32 CLI tests)
• cargo clippy -p robonix-sentinel -p robonix-executor -p robonix-cli --all-targets -- -D warnings
• python3 -m unittest scripts/tests/test_check_commit_authorship.py
• python3 scripts/check_commit_authorship.py --base origin/dev-keystone --head HEAD
• git diff --check

Companion change

The admin rule-management page is being published separately from the robonix-client Keystone branch.

This PR intentionally targets dev-keystone; it does not change dev or dev-next.

[enkerewpo]

Companion Client PR: syswonder/robonix-client#9 (targets feat/keystone-accounts). Please review/land the backend contract before or together with the Client UI.