feat: add hunt/monster domain entities and pure danger-rating helper

Adds Task 1 of Playable Slice 0.2: pure entity/enum/helper definitions
for the Hunt/Encounter system (MonsterDefinition, LocationMonster,
Hunt, HuntEncounter, EncounterType, HuntStatus, RandomSource,
DangerRating). No DB migration, module wiring, or seed data yet.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/api/src/hunting/danger-rating.ts

@@ -0,0 +1,31 @@
+export enum DangerRating {
+  WEAK = 'WEAK',
+  MATCH = 'MATCH',
+  STRONG = 'STRONG',
+  VERY_DANGEROUS = 'VERY_DANGEROUS',
+  DEADLY = 'DEADLY',
+}
+
+export interface CombatantStats {
+  attack: number;
+  armor: number;
+  hp: number;
+}
+
+// power(entity) = attack*4 + armor*2 + floor(hp/5) — a deliberately small,
+// provisional server-side stand-in for a future CombatPower system (none
+// exists yet in this codebase). ratio = monsterPower / characterPower.
+export function calculateDangerRating(
+  character: CombatantStats,
+  monster: CombatantStats,
+): DangerRating {
+  const power = (stats: CombatantStats) =>
+    stats.attack * 4 + stats.armor * 2 + Math.floor(stats.hp / 5);
+  const ratio = power(monster) / power(character);
+
+  if (ratio < 0.65) return DangerRating.WEAK;
+  if (ratio < 1.0) return DangerRating.MATCH;
+  if (ratio < 1.7) return DangerRating.STRONG;
+  if (ratio < 2.3) return DangerRating.VERY_DANGEROUS;
+  return DangerRating.DEADLY;
+}