fix(config): reject non-object raw yaml

[MicroMilo]

Summary

• make parseConfigYaml reject null, array, and primitive YAML roots
• align raw YAML validation with the save path root-type contract
• add focused coverage for non-object raw YAML inputs

Verification

• npm --workspace ui exec vitest run server/services/pilotdeckConfig.raw-yaml.test.js
• npm exec -- tsc --noEmit -p tsconfig.json

Notes

This is a real validate/save mismatch: /api/config/validate could normalize non-object YAML into defaults while the PUT path rejected the same input.