Honor lifecycle dependencies when starting nodes

[orrious]

Summary

Make node startup honor lifecycle dependencies instead of starting every selected node concurrently.

• derive startup ordering from wait-for lifecycle dependencies
• order shared-network-namespace children after their provider
• validate missing dependencies and dependency cycles
• preserve existing behavior for independent nodes by starting them in the same batch
• cover ordering, validation, and external-container dependencies with unit tests

Validation

• Linux Go 1.26.5: go test ./core

[orrious]

Rebased this branch onto current main and force-pushed the updated head.

Current head: cbc2d0b5d

Validation completed on the real lab runners:

• x86 runner: go test ./core passed
• ARM runner: go test ./core passed