docs: update README.md with relationship system documentation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -52,6 +52,7 @@ In follow mode, the camera tracks an NPC and a panel slides in from the right sh
 - Current activity (Wandering, Eating, Resting, Socializing, Idle)
 - Live-updating needs bars (Hunger, Energy) with color-coded fill levels
 - NPC stats in a two-column grid (STR, DEX, CON, INT, PER / SOC, COU, CUR, EMP, TMP)
+- **Relations tab** showing relationships grouped by tier with slider visualization
 
 The panel uses an EarthBound/SNES RPG-inspired aesthetic with doubled borders, pixel font, and smooth slide transitions.
 
@@ -276,9 +277,41 @@ Stats influence gameplay systems:
 - **Perception** extends or shrinks the social awareness radius
 - **Sociability** reduces social interaction cooldowns
 - **Empathy** biases social interactions toward positive outcomes
+- **Courage** influences willingness to interact with disliked NPCs
+- **Curiosity** extends awareness radius for NPCs not yet encountered
 
 Stats also have **transient modifiers** (e.g., low hunger debuffs Intelligence) and **baseline drift** (tiny permanent shifts from experience over time).
 
+## Relationships
+
+NPCs form relationships through social interactions. Each relationship is tracked independently per NPC (asymmetric — A's view of B can differ from B's view of A).
+
+**How it works:**
+- Relationships are lazy-initialized on first encounter (NPCs don't "know" each other until they interact)
+- Each interaction updates relationship values (-100 to 100) based on outcome, with **diminishing returns** on repeated interactions
+- Deltas are **blended asymmetrically**: 30% shared outcome + 70% individual perception
+- Stats influence relationships: **Empathy** boosts positive gains, **Temperament** amplifies negative losses, **Sociability** adds a general bonus and determines friend capacity
+
+**Classification tiers** (derived from value):
+
+| Range | Tier |
+|-------|------|
+| 80 to 100 | Partner |
+| 50 to 79 | Close Friend |
+| 20 to 49 | Friend |
+| 5 to 19 | Acquaintance |
+| -4 to 4 | Stranger |
+| -19 to -5 | Wary |
+| -49 to -20 | Rival |
+| -79 to -50 | Enemy |
+| -100 to -80 | Nemesis |
+
+**Caps:** Partner cap defaults to 1 (2 for high sociability + empathy NPCs). Friend cap scales with sociability.
+
+**Despawn behavior:** Strong relationships (|value| >= 20) persist as **memories** when an NPC is removed. Weaker relationships fade toward zero and are cleaned up.
+
+All relationship tuning values are config-driven in `server/src/config/relationshipConfig.ts`, designed for future admin UI integration.
+
 ## Game Constants
 
 All tunable game constants live in `shared/src/constants.ts`: