test(stack): prove Nacos watch refresh

[XnLemon]

Summary

• enable the Router's Nacos gRPC observation path in the assembled backend
• replace the only ready Runtime B instance between two Invocations without restarting the Router
• require the next Invocation to consume the pushed topology and reach the replacement instance
• pin Core and contract identity to the exact watch-consumption revision
• include the watch profile service in metadata-only log scanning and backend CI cleanup

This proves lazy per-Release observation and pushed topology refresh across Invocations through real Nacos 2.5.1 and the Samples registration adapter.

Validation

• go test ./...
• docker compose --file compose.yaml config --no-interpolate --quiet
• git diff --check
• go test -tags=e2e -count=1 ./tests/backend against a fresh local Nacos/PostgreSQL assembly

The backend acceptance passed in 37.981s, including JSON/SSE routing, the real Nacos watch transition, nested calls, failure semantics, Router restart, Ledger checks, and metadata-only storage/log checks.

Fallback

Fallback delta: removed 0, retained 0, added 0, net 0

Added fallback evidence: none