feat(combat): validate potions, persist telegraph state, and expose both on the combat DTO

Also updates the pre-existing exact-equality playerState assertion in
combat-equipment-integration.spec.ts, which broke from the new
potionsRemaining field but wasn't listed in the task brief's file scope.

apps/api/src/combat/combat-equipment-integration.spec.ts

@@ -369,7 +369,12 @@ describe('equipping Räuberklinge increases combat damage (spec §45, §60)', ()
 
     // The finished combat's playerState snapshot (written once at startCombat)
     // must not be retroactively rewritten by equipping after the fight ends.
-    expect(state.combats[0].playerState).toEqual({ attack: 6, weaponDamage: 8, armor: 0 });
+    expect(state.combats[0].playerState).toEqual({
+      attack: 6,
+      weaponDamage: 8,
+      armor: 0,
+      potionsRemaining: 2,
+    });
 
     const reloaded = await combatService.getCombat(CHARACTER_ID, combat.id);
     expect(reloaded.status).toBe(result.status);