Preference calibration

Preference calibration routes help Achiral improve learned preferences with explicit feedback and targeted calibration.

Routes

Method	Path	Purpose
POST	/api/memory/preferences/:id/feedback	Attach feedback to a learned preference.
GET	/api/memory/preferences/low-confidence	Return preferences that need calibration.
POST	/api/memory/preferences/calibrate	Run preference calibration.
GET	/api/memory/preferences/feedback-stats	Return preference feedback statistics.

These are workspace routes protected by session auth and memory permissions.