Add hit_processing.py: HitProcessor with model_opt (LLM-generated) and direct (concatenated chunks) modes, with in-process cache
Add settings.py: KBSettings/KBSettingsUpdate models, KBSettingsStore with async CRUD
Add KB settings endpoints to kb_management.py: GET/PUT /kb-management/kbs/{kb_id}/settings with owner-only modification
Tests: 43 new tests (25 hit_processing + 18 settings), 293 total passing
chiguyong