Existing honcho.json configs without an explicit observationMode now
default to 'unified' (the old default) instead of being silently
switched to 'directional'. New installations get 'directional' as
the new default.
Detection: _explicitly_configured (host block exists or enabled=true)
signals an existing config. When true and no observationMode is set
anywhere in the config chain, falls back to 'unified'. When false
(fresh install), uses 'directional'.
Users who explicitly set observationMode or granular observation
booleans are unaffected — explicit config always wins.
5 new tests covering all migration paths.
583d9f9597