Deliver incremental router outcomes and complete coverage #1044

Parent: #1041

Deliverable: a supported service execution API that emits each completed router outcome promptly and finishes with complete coverage from one discovery snapshot.

Reuse Galactic's router discovery, node RPCs, and existing diagnostic implementations. Keep node diagnostic RPCs unary; this milestone streams completed router observations, not individual traceroute hops. Define expected and omitted routers from the fixed snapshot so the result cannot silently hide unavailable or unselected routers.

Work items:

• Extend the gateway runner and service RPC to emit completed outcomes without waiting for the slowest router.
• Return router identity, sample time, typed errors, and terminal expected/successful/failed/omitted coverage using the agreed counting rules.
• Expose supported capabilities and publish generated consumer API artifacts; preserve existing unary operator and FabricQuery behavior.
• Add mixed-speed, partial-failure, no-router, omitted-router, truncated-result, and compatibility tests.

Dependencies: #1042, #1043.

Acceptance: A fast router's observation arrives while another router is still executing. Final coverage reconciles with the discovery snapshot, each completed selected router has one outcome, and packet loss or unanswered hops remain observations. A consumer built against the published API can decode the stream. Existing operator and FabricQuery tests continue to pass.