Wire fog-node conformance stub into runnable lane

[mdheller]

Turn the merged fog-node contract stub and checker into a real contract lane.

Scope:

• integrate contracts/fog-node.contract.json into the repo’s expected lane/runner layout
• wire tools/check_fog_node.py into validation flows
• define expected evidence outputs for fog-node checks
• add CI example(s) for a fog conformance run

Acceptance:

• fog-node is represented as a first-class lane/profile in the repo
• validator execution path is documented and testable
• evidence outputs are clear enough for downstream policy/automation use