feat(ops): create action request API with audit trail

[05F3759DF]

Context

Operators need to trigger pre-registered robot-side actions from Keystone, but Keystone must not accept arbitrary commands or bypass auditability. Action requests should reference an allowlisted action ID and validated arguments only.

Scope

• Add an action request model with request_id, robot_id, action_id, args, status, requested_by, requested_at, expires_at, and audit metadata.
• Create an API for operators or services to submit action requests against a robot action catalog entry.
• Validate arguments against the catalog-provided schema before accepting a request.
• Enforce RBAC and approval requirements for high-risk actions.
• Write audit events for request creation, approval, cancellation, and status changes.
• Prevent arbitrary shell commands or unmanaged script paths from being submitted.

Acceptance Criteria

• Valid action requests are persisted with a stable request ID.
• Unknown action IDs, invalid arguments, unauthorized users, and expired approval flows are rejected clearly.
• All request lifecycle changes are auditable with the requesting user and robot identity.
• The API never accepts raw shell commands as request payload.
• Tests cover successful creation, schema validation failure, RBAC denial, approval-required actions, and audit log creation.

Depends On

• feat(ops): add robot action catalog model and API #65

Related

• feat(agent): execute allowlisted action requests safely axon#91
• feat(agent): persist action execution state and idempotency axon#92