When a MeshEnvelope is delivered locally and its payload starts with a
known FAPP wire tag (0x01-0x05), MeshNode.process_incoming now delegates
to FappRouter instead of returning a raw Deliver action. Nodes without
FAPP capabilities still receive FAPP-tagged payloads as normal Deliver
actions, preserving backward compatibility.
Adds IncomingAction::Fapp variant, is_fapp_payload() helper, and three
integration tests covering the routing, passthrough, and no-router cases.
Christian Nennemann
fb6b80c81c