8-state NPC mood FSM driven by stress, time of day, and interaction events.
Adds MoodState component, derive_mood() pure function, and update_mood() Bevy
system wired into NpcPlugin. Adds Focused as 9th Mood content tag (D-035
Sprint 8 amendment). Syncs CurrentMood for Layer 4 dialogue selection.
31 unit tests covering priority ordering, boundary conditions, and system
integration. All random values route through SimRng (D-010 determinism).
No floats. No HashMap.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>