Core: correct history for conditioning-exposure changes (correctConditioningExposure) #99

From #91 (@bpodwinski).

Feature: correctConditioningExposure (default false). It applies the conditioning exposure ratio (this frame's vs the history's) in the linear history correction, the way host pre-exposure is already corrected (DeltaPreExposure, validated on Q11).

Why it might matter: history is stored as x/(1+x) of pre-exposed colour. When auto-exposure (or a provided exposure) changes between frames, old history decodes at the new exposure. The 1/16-stop adaptation dead-band (CLAUDE.md, auto-exposure section) hides small changes. Larger steps re-condition history, and per the drift-lag notes that masks 30–45% of lag under auto-exposure.

Before taking it:

• Measure on Q11 (host pre-exposure), Q15 (lighting drift) and a forced exposure step: ghosting and lag, with it on vs off.
• Check the interaction with the dead-band and EXPOSURE_MAX 8.
• Off must be byte-identical.
• If it's a clear win, consider making it the default instead of an option.